Image encoding method and apparatus, and image decoding method and apparatus

ABSTRACT

Provided is a method of decoding motion information characterized in that information for determining motion-related information includes spatial information and time information, wherein the spatial information indicates a direction of spatial prediction candidates used for sub-units from among spatial prediction candidates located on a left side and an upper side of a current prediction unit, and the time information indicates a reference prediction unit of a previous picture used for prediction of the current prediction unit. Further, an encoding apparatus or a decoding apparatus capable of performing the above described encoding or decoding method may be provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation application of U.S. patent application Ser. No.16/077,392 filed on Aug. 10, 2018, which is a National Stage Entry ofInternational Application No. PCT/KR2017/001535 filed Feb. 13, 2017,which claims benefit of Provisional Patent Application No. 62/294,417filed Feb. 12, 2016, the disclosure of which is incorporated herein inits entirety by reference.

TECHNICAL FIELD

The present disclosure relates to methods and apparatuses for encodingor decoding an image by using various data units included in the image,and more particularly, to a method of adaptively selecting a transformkernel based on a transform shape (a transform size and a shape such asa square shape, a non-square shape, or an arbitrary shape) in a videocompression codec.

BACKGROUND ART

A general video compression codec uses a method of compressing a videoby applying a transform to a residual signal obtained via intraprediction or inter prediction and then performing quantization andentropy coding on a transform coefficient. A transform shape is a squareshape, and a discrete cosine transform (DCT) kernel or a kernel in whicha DCT is approximated to an integer transform is generally used as atransform kernel. For example, recently, a high efficiency video coding(HEVC) codec adopts a square integer transform having a size of 4×4,8×8, 16×16, or 32×32, and the square integer transform is obtained byapproximating a DCT. However, HEVC uses an integer transform obtained byapproximating a discrete sine transform (DST) only for a residual signalhaving a size of 4×4 exclusively obtained via intra prediction.

Recently, the joint video experts team (JVET) and others have activelyexplored technology for next generation video codec standardizationsince HEVC, and new transform technologies have been introduced. Forexample, adaptive multiple transformation (AMT) is a method of selectinga kernel to be used for a current transform unit (TU) from among aplurality of pre-defined candidate transform kernels, applying theselected kernel to the current TU, and additionally transmittinginformation about the selected kernel. In this case, the set ofcandidate transform kernels are fixed in a coding unit (CU) to whichinter prediction is applied, and vary according to an inter predictionmode in a CU to which intra prediction is applied. In addition, a numberof secondary transform technologies of applying a transform again to atransform coefficient obtained after primary transformation have beenproposed. For example, rotational transformation (ROT) involvessplitting a transform coefficient into 4×4 units, selecting one fromamong pre-determined secondary transforms, and applying the selectedsecondary transform to the 4×4 units. In non-separable secondarytransformation (NSST) that operates like ROT, a transform kernel isnon-separable and secondary transform kernel candidates to be appliedvary based on an intra prediction mode like in AMT.

DESCRIPTION OF EMBODIMENTS Technical Problem

In conventional inter prediction technology, since one motion vector isassigned per block, prediction is performed, and a smaller block iscompressed when there are various movements in blocks, more bits arerequired. Also, since one motion vector is used even when there aredifferent objects in the same block, prediction accuracy is reduced.

Solution to Problem

Conventional technology has an advantage in that compression efficiencymay be improved by adaptively selecting and using a transform kernelaccording to residual signal characteristics in a current transform unit(TU), but has a disadvantage in that since it is assumed that a squaretransform is used in all cases, the conventional technology is notapplicable when a non-square or arbitrary transform is used.

There may be provided a video encoding method according to an embodimentincluding: generating a residual block including a residual signal for acurrent coding unit, based on a prediction signal generated byprediction with respect to the current coding unit; and performingtransformation on the residual signal by applying a transform kernelhaving a predetermined size corresponding to a size of the residualblock, wherein the performing of the transformation includes: obtainingtransform shape information about the size or a shape of the residualblock; and adaptively determining the transform kernel based on thetransform shape information.

There may be provided a video decoding method according to an embodimentincluding: obtaining encoded data of a current coding unit from amongcoding units of an encoded current picture and transform shapeinformation about a size or a shape of a residual block including aresidual signal with respect to the current coding unit from a parsedbitstream; adaptively determining a transform kernel based on thetransform shape information; generating a residual signal for thecurrent coding unit by performing transformation on the current codingunit by using the determined transform kernel; and performing decodingbased on the residual signal with respect to the current coding unit.

There may be provided a video decoding apparatus according to anembodiment including: a receiver configured to receive and parse abitstream with respect with an encoded data; an extractor configured toextract the encoded data of a current coding unit from among codingunits for encoding a current picture of encoded video and transformshape information about a size or a shape of a residual block includinga residual signal with respect to the current coding unit from a parsedbitstream; a transform kernel selector configured to adaptivelydetermine a transform kernel based on the transform shape information todecode the encoded data; a transformer configured to generate theresidual signal for the current coding unit by performing transformationon the current coding unit by using the determined transform kernel; anda decoder configured to performing decoding based on the residual signalwith respect to the current coding unit.

Advantageous Effects of Disclosure

According to various embodiments of the present disclosure, since atransform kernel is adaptively selected based on a transform shape(e.g., a square shape, a non-square shape, or an arbitrary shape), inaddition to information that is typically used such as an intraprediction mode, compression efficiency may be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an encoding apparatus including a transformkernel selector that adaptively selects a transform kernel based on atransform shape and a transformer, according to an embodiment.

FIG. 2 is a block diagram of a decoding apparatus including a transformkernel selector that adaptively selects a transform kernel based on atransform shape, and an inverse transformer, according to an embodiment.

FIG. 3 illustrates a transform shape applicable during a transform,according to an embodiment.

FIG. 4 illustrates that a transform kernel is assigned according towhether separation is vertical separation or horizontal separation,according to an embodiment.

FIG. 5 is a block diagram of a transform kernel selector including atransform kernel candidate deriver and a transform kernel determiner,according to an embodiment.

FIG. 6 illustrates information about an intra prediction mode accordingto an embodiment.

FIG. 7A is a flowchart of a process of deriving transform kernelcandidates when prediction is intra prediction, according to anembodiment.

FIG. 7B is a flowchart of a process of deriving transform kernelcandidates when prediction is not intra prediction, according to anembodiment.

FIG. 8 is a flowchart of a method of performing transformation byadaptively selecting a transform kernel selector at an encoding end,according to an embodiment.

FIG. 9 is a flowchart of a method of performing transformation byadaptively selecting the transform kernel selector at a decoding end,according to an embodiment.

FIG. 10 illustrates that shapes into which second coding units may besplit are restricted when the second coding units having a non-squareshape split and determined from a first coding unit satisfy apredetermined condition, according to an embodiment.

FIG. 11 illustrates a process of splitting a coding unit having a squareshape when split shape information is unable to indicate that a codingunit is split into four square shapes, according to an embodiment.

FIG. 12 illustrates that an order of processing a plurality of codingunits may vary according to a process of splitting a coding unit,according to an embodiment.

FIG. 13 illustrates a process of determining a depth of a coding unitaccording to a change in a shape and a size of the coding unit when aplurality of coding units are determined as the coding unit isrecursively split, according to an embodiment.

FIG. 14 illustrates a part index (PID) for distinguishing depths andcoding units that may be determined according to shapes and sizes ofcoding units, according to an embodiment.

FIG. 15 illustrates that a plurality of coding units are determinedaccording to a plurality of predetermined data units included in apicture, according to an embodiment.

FIG. 16 illustrates a processing block that becomes a criterion fordetermining a determining order of reference coding units included in apicture, according to an embodiment.

FIG. 17 illustrates coding units that may be determined for each picturewhen combinations of shapes into which a coding unit may be split aredifferent, according to an embodiment.

FIG. 18 illustrates various shapes of a coding unit that may bedetermined based on split shape information that may be represented as abinary code, according to an embodiment.

FIG. 19 illustrates other shapes of a coding unit that may be determinedbased on split shape information that may be represented as a binarycode, according to an embodiment.

FIG. 20 is a block diagram of an image encoding and decoding system forperforming loop filtering.

FIG. 21 illustrates an example of filtering units included in a largestcoding unit and filtering performance information of a filtering unit,according to an embodiment.

FIG. 22 illustrates a process of performing a merge operation or a splitoperation on coding units determined according to a predeterminedencoding method, according to an embodiment.

FIG. 23 illustrates an index according to a Z-scan order of a codingunit, according to an embodiment.

FIG. 24 illustrates a reference sample for intra prediction of a codingunit, according to an embodiment.

BEST MODE

There may be provided a video encoding method according to an embodimentincluding: generating a residual block including a residual signal for acurrent coding unit, based on a prediction signal generated byprediction with respect to the current coding unit; and performingtransformation on the residual signal by applying a transform kernelhaving a predetermined size corresponding to a size or a shape of theresidual block, wherein the performing of the transformation includes:obtaining transform shape information about the size or a shape of theresidual block; and adaptively determining the transform kernel based onthe transform shape information.

According to an embodiment, the transform shape information may includeinformation about a shape indicating whether the shape of the residualblock is a square shape, a non-square shape, or an arbitrary shape.

According to an embodiment, there may be provided a video encodingmethod including: determining whether the transformation is performed byseparating the residual signal in a vertical direction and a horizontaldirection; and when the transformation is performed by separating theresidual signal in the vertical direction and the horizontal direction,adaptively determining the transform kernel based on the transform shapeinformation in each of the vertical direction and the horizontaldirection.

According to an embodiment, there may be provided a video encodingmethod including: obtaining prediction information indicating whetherthe residual signal is obtained by intra prediction; when the residualsignal is obtained by the intra prediction, obtaining information aboutan intra prediction mode used in the intra prediction; and when theresidual signal is obtained by the intra prediction, determining thetransform kernel based on the information about the intra predictionmode.

According to an embodiment, there may be provided a video encodingmethod including: obtaining transform kernel candidates based on thetransform shape information; obtaining a transform kernel indexindicating a transform kernel used in the transformation from among thetransform kernel candidates; and determining the transform kernel usedin the transformation from among the transform kernel candidates basedon the transform kernel index.

There may be provided a video decoding method according to an embodimentincluding: obtaining encoded data of a current coding unit from amongcoding units for encoding a current picture of an encoded video andtransform shape information about a size or a shape of a residual blockincluding a residual signal with respect to the current coding unit,from a parsed bitstream; adaptively determining a transform kernel basedon the transform shape information to decode the encoded data;generating the residual signal for the current coding unit by performingtransformation on the current coding unit by using the determinedtransform kernel; and performing decoding based on the residual signalwith respect to the current coding unit.

According to an embodiment, the transform shape information may includeinformation about a shape indicating whether the shape of the residualblock is a square shape, a non-square shape, or an arbitrary shape.

According to an embodiment, there may be provided a video decodingmethod including: determining whether the transformation is performed byseparating the residual signal in a vertical direction and a horizontaldirection; and when the transformation is performed by separating theresidual signal in the vertical direction and the horizontal direction,adaptively determining the transform kernel based on the transform shapeinformation in each of the vertical direction and the horizontaldirection.

According to an embodiment, there may be provided a video decodingmethod including: obtaining prediction information indicating whetherthe residual signal is obtained by intra prediction from the bitstream;when the residual signal is obtained by the intra prediction, obtaininginformation about an intra prediction mode used in the intra predictionfrom the bitstream; and when the residual signal is obtained by theintra prediction, determining the transform kernel based on theinformation about the intra prediction mode.

According to an embodiment, there may be provided a video decodingmethod including: obtaining transform kernel candidates based on thetransform shape information; obtaining a transform kernel indexindicating a transform kernel used in the transformation from among thetransform kernel candidates; and determining the transform kernel usedin the transformation from among the transform kernel candidates basedon the transform kernel index.

There may be provided a video decoding apparatus according to anembodiment including: a receiver configured to receive and parse abitstream for an encoded video; an extractor configured to extractencoded data of a current coding unit from among coding units that aredata units for encoding a current picture of the encoded video andtransform shape information about a size or a shape of a residual blockwith respect to the current coding unit, from the parsed bitstream; atransform kernel selector configured to adaptively determine a transformkernel based on the transform shape information to decode the encodeddata; a transformer configured to generate the residual signal for thecurrent coding unit by performing transformation on the current codingunit by using the determined transform kernel; and a decoder configuredto perform decoding based on the residual signal with respect to thecurrent coding unit.

According to an embodiment, the transform shape information may includeinformation about a shape indicating whether the shape of the residualblock is a square shape, a non-square shape, or an arbitrary shape.

According to an embodiment, the transform kernel selector may be furtherconfigured to: determine whether the transformation is performed byseparating the residual signal in a vertical direction and a horizontaldirection; and when the transformation is performed by separating theresidual signal in the vertical direction and the horizontal direction,adaptively determine the transform kernel based on the transform shapeinformation in each of the vertical direction and the horizontaldirection.

According to an embodiment, the transform kernel selector may be furtherconfigured to: obtain, from the bitstream, prediction informationindicating whether the residual signal is obtained by intra prediction;when the residual signal is obtained by the intra prediction, obtaininformation about an intra prediction mode used in the intra predictionfrom the bitstream; and when the residual signal is obtained by theintra prediction, determine the transform kernel based on theinformation about the intra prediction mode.

According to an embodiment, the transform kernel selector may include: atransform kernel candidate deriver configured to obtain transform kernelcandidates based on the transform shape information; and a transformkernel determiner configured to obtain a transform kernel indexindicating a transform kernel used in the transformation from among thetransform kernel candidates and generate transform kernel informationused in the transformation from among the transform kernel candidatesbased on the transform kernel index.

There may be provided a video encoding apparatus according to anembodiment including: a transformer configured to generate a residualblock including a residual signal for a current coding unit, based on aprediction signal generated by prediction for the current coding unit,and perform a transform on the residual signal by applying a transformkernel having a predetermined size corresponding to a size of theresidual block; and a transform kernel selector configured to obtaintransform shape information about the size or a shape of the residualblock, and adaptively determine the transform kernel based on thetransform shape information.

According to an embodiment, the transform shape information may includeinformation about a shape indicating whether the shape of the residualblock is a square shape, a non-square shape, or an arbitrary shape.

According to an embodiment, when it is determined whether thetransformation is performed by separating the residual signal in avertical direction and a horizontal direction and when thetransformation is performed by separating the residual signal in thevertical direction and the horizontal direction, the transform kernelmay be adaptively determined based on the transform shape information ineach of the vertical direction and the horizontal direction.

According to an embodiment, there may be provided a video encodingapparatus characterized by: obtaining prediction information indicatingwhether the residual signal is obtained by intra prediction; when theresidual signal is obtained by the intra prediction, obtaininginformation about an intra prediction mode used in the intra prediction;and when the residual signal is obtained by the intra prediction,determining the transform kernel based on the information about theintra prediction mode.

According to an embodiment, there may be provided a video encodingapparatus characterized by obtaining transform kernel candidates basedon the transform shape information; obtaining a transform kernel indexindicating a transform kernel used in the transformation from among thetransform kernel candidates; and determine the transform kernel used inthe transformation from among the transform kernel candidates based onthe transform kernel index.

Mode of Disclosure

Advantages and features of the present disclosure and methods ofaccomplishing the same may be understood more readily by reference tothe following detailed description of embodiments and the accompanyingdrawings. In this regard, the present embodiments may have differentforms and should not be interpreted as being limited to the descriptionsset forth herein. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete and will fully convey the scopeof the present disclosure to one of ordinary skill in the art.

Hereinafter, the terms used in the specification will be brieflydefined, and the present disclosure will be described in detail.

The terms used in the present disclosure are those general termscurrently widely used in the art in consideration of functions in thepresent disclosure, but the terms may vary according to the intention ofone of ordinary skill in the art, precedents, or new technology in theart. Also, some of the terms used herein may be arbitrarily chosen bythe present applicant. In this case, these terms are defined in detailbelow. Accordingly, the specific terms used herein should be understoodbased on the unique meanings thereof and the whole context of thepresent disclosure.

As used herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise

Throughout the specification, when a portion “includes” an element,another element may be further included, rather than excluding theexistence of the other element, unless otherwise described. Also, theterm “unit” used herein means a software component or a hardwarecomponent such as a field-programmable gate array (FPGA) or anapplication-specific integrated circuit (ASIC), and performs a specificfunction. However, the term “unit” is not limited to software orhardware. The “unit” may be formed so as to be in an addressable storagemedium, or may be formed so as to operate one or more processors. Thus,for example, the term “unit” may refer to components such as softwarecomponents, object-oriented software components, class components, andtask components, and may include processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,micro codes, circuits, data, a database, data structures, tables,arrays, or variables. A function provided by the components and “units”may be associated with the smaller number of components and “units”, ormay be divided into additional components and “units”.

Hereinafter, an “image” may denote a still image of a video, or a movingimage, i.e., a video itself.

Hereinafter, a “sample” denotes data that is assigned to a samplinglocation of an image and is to be processed. For example, pixels in animage of a spatial domain or transform coefficients in a transformdomain may be samples. A unit including one or more samples may bedefined as a block.

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the attached drawings in order to enable one ofordinary skill in the art to embody and practice the present disclosure.Parts in the drawings unrelated to the detailed description are omittedto ensure clarity of the present disclosure.

FIG. 1 is a block diagram of an encoding apparatus including a transformkernel selector 120 that adaptively selects a transform kernel based ona transform shape, and a transformer 110, according to an embodiment.

Referring to FIG. 1, when a residual signal is applied to thetransformer 110, the transformer 110 may perform transformation. Also,the transform kernel selector 120 may determine transform kernelinformation about a transform kernel to be applied to the residualsignal and may transmit the transform kernel information as an input tothe transformer 110.

According to an embodiment, the transform kernel selector 120 mayreceive transform shape information as a basic input. For example, thetransform shape information may include information about a size and ashape of a current transform. In more detail, the transform shapeinformation about the shape may include information about whether atransform shape is a square shape, a non-square shape, or an arbitraryshape. Also, when the transform shape is a non-square shape or anarbitrary shape, the transform shape information about the shape mayinclude information about a detailed shape (e.g., a horizontal orvertical length). The transform shape information about the size mayinclude information about vertical and horizontal lengths of a squaretransform, a non-square transform, or an arbitrary transform. Also, whenthe transform shape is an arbitrary shape, the transform shapeinformation about the size may further include information about adiagonal length.

According to an embodiment, the transform kernel selector 120 mayreceive, as an input, information indicating whether the residual signalapplied as a current input is a signal obtained by performing intraprediction. For example, the transform kernel selector 120 may receive,as an input, prediction information indicating whether the residualsignal applied as the current input is a signal obtained by performingintra prediction. The prediction information may indicate whether theresidual signal applied as the current input is a signal obtained byperforming intra prediction or a signal obtained by performing interprediction.

According to an embodiment, when the input residual signal is obtainedby intra prediction, the transform kernel selector 120 may obtaininformation (i.e., intra prediction mode information) about an intraprediction mode used in the intra prediction. For example, the intraprediction mode may indicate an index in an Intra DC mode, an IntraPlanar mode, and an Intra Angular mode. When the input residual signalis obtained by inter prediction, the transform kernel selector 120 maynot receive the intra prediction mode information as an input.

Examples of the intra prediction mode for a luminance component mayinclude the Intra Planar mode, the Intra DC mode, and the Intra Angularmode. In more detail, in the Intra Planar mode, a prediction value maybe generated by averaging values obtained by performing linearinterpolation (interpolation using a weight according to a distance) inhorizontal and vertical directions on values obtained by copyingreference pixels. Also, in the Intra DC mode, an average value ofneighboring pixels of a current block may be used as a prediction value.Prediction in the Intra DC mode may be performed by filtering sampleslocated at a boundary of a prediction block in order to removediscontinuity between a prediction sample and reference samples, withoutusing an average value for a block to be predicted as the predictionsample. Also, in the Intra Angular mode, a prediction sample may beobtained in consideration of directionality when the prediction sampleis calculated from reference samples. Directionality according to eachmode in the Intra Angular mode will be described below with reference toFIG. 6.

Also, examples of the intra prediction mode for a chrominance componentmay include the Intra DC mode, an Intra Vertical mode, anIntra-Horizontal mode, and an Intra DM mode. The modes other than theIntra DM mode may generate a prediction sample by using the same processas the method described for the luminance component. In the Intra DMmode, a mode of a chrominance component may be used as the same mode asthat of a luminance component by using the feature that the luminancecomponent and the chrominance component are similar to each other.

According to an embodiment, the transformer 110 may apply a transform tothe residual signal based on the transform kernel information determinedand transmitted as an input by the transform kernel selector 120, andthen may output a transform coefficient as a result of thetransformation.

For example, the transform kernel selector 120 may adaptively select atransform kernel based on at least one of the transform shapeinformation and the intra prediction mode information. For example, thetransform kernel selector 120 may send the transform kernel informationabout the adaptively selected transform kernel to the transformer 110.In this case, the transformer 110 may perform transformation on theresidual signal by applying the selected transform kernel based on thereceived transform kernel information. A kernel that is a discretecosine transform (DCT) or approximates a DCT to an integer transform maybe used as the transform kernel, and when the residual signal is asignal having a size of 4×4 obtained by intra prediction, a kernelobtained by approximating a discrete sine transform (DST) may be used.For example, types of the transform kernel may include transform kernelsobtained by integerizing DCT-5, DCT-8, DST-1, and DST-7 transforms.Also, when the residual signal is a signal to which intra prediction isapplied, types of the transform kernel may include a transform kernelobtained by offline training for each intra prediction mode andtransform shapes. Also, when the residual signal is a signal to whichinter prediction is applied, types of the transform kernel may include atransform kernel obtained by offline training according to eachtransform shape besides DCT and DST transforms. The types of thetransform kernel are merely examples, and the present disclosure is notlimited thereto.

For example, the transform kernel selector 120 may select a kernel to beused for a current transform unit (TU) from among a plurality ofpre-defined candidate transform kernels, may apply the selected kernel,and may additionally transmit information about the selected kernel. Inthis case, the set of candidate kernels may be fixed in a coding unit towhich inter prediction is applied, and may vary according to aprediction mode in a coding unit to which intra prediction is applied.Also, for example, the transformer 110 may perform secondarytransformation where a transform is applied again to a transformcoefficient obtained after primary transformation. In more detail,rotational transformation (ROT) may involve splitting a transformcoefficient into 4×4 units, selecting one from among pre-determinedsecondary transformations, and applying the selected secondarytransform. Also, in non-separable secondary transformation (NSST) thatoperates like the ROT, a transform kernel may be non-separable andsecondary transform kernel candidates to be applied may vary based on anintra prediction mode.

FIG. 3 illustrates a transform shape applicable during transformationaccording to an embodiment.

According to an embodiment, an image decoding apparatus may split acoding unit into various shapes by using block shape information andsplit shape information obtained by a bistream obtainer. Shapes intowhich the coding unit may be split may correspond to various shapesincluding shapes described with reference to the above embodiments.

According to an embodiment, a shape of a residual block may be a squareshape obtained by splitting a coding unit having a square shape in atleast one of a horizontal direction and a vertical direction, or may bea non-square shape obtained by splitting a coding unit having anon-square shape into the horizontal direction or the verticaldirection.

According to an embodiment, transform shape information may berepresented as a two-digit binary code, and a binary code may beassigned to each transform shape. For example, when a coding unit is notsplit, the transform shape information may be represented as (00)b; whena coding unit is split in the horizontal direction and the verticaldirection, the transform shape information may be represented as (01)b;when a coding unit is split in the horizontal direction, the transformshape information may be represented as (10)b; and when a coding unit issplit in the vertical direction, the transform shape information may berepresented as (11)b.

Also, for example, a coding unit may be split into two coding units, andin this case, the transform shape information may be represented as(10)b. Also, a coding unit may be split into three coding units, and inthis case, the transform shape information may be represented as (11)b.Also, it may be determined that a coding unit is not split, and in thiscase, the transform shape information may be represented as (0)b. Inorder to use a binary code indicating the transform shape information,variable length coding (VLC), instead of fixed length coding (FLC), maybe used.

FIG. 4 illustrates that a transform kernel is assigned according towhether separation is vertical separation or horizontal separationaccording to an embodiment.

According to an embodiment, the transform kernel selector 120 maydetermine a shape of a residual block (i.e., a transform is a squaretransform or a non-square transform), and may determine whether thetransformation may be performed by separating a residual signal in avertical direction and a horizontal direction. For example, thetransform kernel selector 120 may include the feature that the residualsignal is separable in transform kernel information and may send thetransform kernel information to a transformer.

According to an embodiment, when the feature that the residual signal isseparable is included, the transform kernel selector 120 may determineto select each transform kernel based on transform shape information ofthe residual signal in each of the vertical direction and the horizontaldirection.

For example, when transform kernel information about a residual block410 includes the feature that a transform is a square transform or anon-square transform and is separable, the transform kernel informationmay include information about a transform kernel to be applied in eachof the vertical and horizontal directions. In contrast, when a transformis a square transform or a non-square transform and is non-separable orwhen a transform is an arbitrary transform, like in a residual block420, the transform kernel information may include information about onetransform kernel irrespective of an application direction.

FIG. 5 is a block diagram of a transform kernel selector including atransform kernel candidate deriver 510 and a transform kernel determiner520 according to an embodiment.

According to an embodiment, the transform kernel selector may includethe transform kernel candidate deriver 510 and the transform kerneldeterminer 520. The transform kernel candidate deriver 510 may receive,as an input, transform shape information and intra prediction modeinformation, and may derive transform kernel candidates to be applied toa current residual signal. The intra prediction mode information may besent to the transform kernel candidate deriver 510 only when the currentresidual signal is obtained by intra prediction.

According to an embodiment, the transform kernel candidates may includeone or more sets of transform kernel candidates. For example, transformkernels obtained by integerizing DCT-5, DCT-8, DST-1, and DST-7transforms may be included in the transform kernel candidates. Also,when the residual signal is a residual signal to which intra predictionis applied, a transform kernel obtained by offline training for eachintra prediction mode and transform shapes may be included in thetransform kernel candidates. Also, when the residual signal is aresidual signal to which inter prediction is applied, a transform kernelobtained by offline training according to each transform shape besidesDCT and DST transforms may be included in the transform kernelcandidates. The transform kernel candidates may be merely examples, andthe present disclosure is not limited thereto.

The transform kernel determiner 520 may receive, as an input, thetransform kernel candidates from the transform kernel candidate deriver510, may receive, as an input, a transform kernel index from abitstream, may determine a transform kernel to be applied to the currentresidual signal, and may send transform kernel information to atransformer.

According to an embodiment, the transform kernel index may include indexinformation about a kernel to be applied to the current residual signalfrom among the plurality of transform kernel candidates. For example,the transform kernel index may be applied, as an input, only when thetransform kernel candidates include a plurality of sets of transformkernel candidates, and the transform kernel index may be included in thebitstream as described above. For example, when the number of thetransform kernel candidates output by the transform kernel candidatederiver 510 is 1, the transform kernel determiner 520 may determine thesingle input as a transform kernel, and may send transform kernelinformation to the transformer. For example, when a transform is asquare transform or a non-square transform and is separable, a processof deriving transform kernel candidates and determining a transformkernel may be performed in each of a vertical direction and a horizontaldirection, and transform kernel information about vertical andhorizontal transforms may be output.

FIG. 6 illustrates information about an Intra-Angular mode from amongintra prediction modes according to an embodiment.

According to an embodiment, new 67 prediction modes obtained by adding32 prediction modes 620 to existing 35 prediction modes 610 may beincluded in the Intra-Angular mode from among the intra predictionmodes.

For example, when intra prediction is performed by using both left andtop data units 630 or right and bottom data units 640 according to theintra prediction mode, a transform kernel selector may obtain intraprediction mode information used in each intra prediction, and mayselect a transform kernel based on each obtained intra prediction modeinformation.

According to an embodiment, the intra prediction mode may indicate anindex in an Intra DC mode, an Intra Planar mode, and an Intra Angularmode.

FIGS. 7A and 7B are flowcharts of a process of deriving transform kernelcandidates according to an embodiment.

FIG. 7A is a flowchart of a process of deriving transform kernelcandidates when a current residual signal is a signal obtained by intraprediction.

According to an embodiment, it may be determined whether a shape of acurrent residual block is a rectangular shape (e.g., a square shape or anon-square shape) or an arbitrary shape based on transform shapeinformation that is received as an input.

In more detail, in operation S711, it may be determined whether a shapeof a current residual block is a rectangular shape based on transformshape information received as an input, and when the shape is arectangular shape, in operation S712, it may be determined whether theshape is a square shape or a non-square shape. In contrast, when it isdetermined in operation S711 based on the transform shape informationreceived as an input that the shape of the current residual block is nota rectangular shape, it may be determined that the shape of the currentresidual block is an arbitrary shape.

According to an embodiment, when it is determined based on the transformshape information that the shape of the current residual block is arectangular shape (i.e., a square shape or a non-square shape), it maybe determined whether a transform is separable or non-separable in eachof a vertical direction and a horizontal direction.

In more detail, when the shape of the current residual block is a squareshape, in operation S713, it may be determined whether the transform isseparable. When the shape of the current residual block is a non-squareshape, in operation S714, it may be determined whether the transform isseparable. For example, when the transform is separable in each of thevertical direction and the horizontal direction, transform kernelcandidates in each of the vertical direction and the horizontaldirection may be derived.

According to an embodiment, when the transform shape information andwhether the transform is separable are determined, the transform kernelcandidates may be determined based on the transform shape informationand whether the transform is separable.

In more detail, when the shape of the current residual block is a squareshape and the transform is separable, in operation S715, a transformkernel selector may obtain the transform kernel candidates in each ofthe vertical direction and the horizontal direction based on an intraprediction mode. When the shape of the current residual block is asquare shape and the transform is non-separable, in operation S716, thetransform kernel selector may obtain the transform kernel candidatesbased on the intra prediction mode. When the shape of the currentresidual block is a non-square shape and the transform is separable, inoperation S717, the transform kernel selector may obtain the transformkernel candidates in each of the vertical direction and the horizontaldirection based on the intra prediction mode and vertical and horizontallengths of a non-square transform. When the shape of the currentresidual block is a non-square shape and the transform is non-separable,in operation S718, the transform kernel selector may obtain thetransform kernel candidates based on the intra prediction mode and thevertical and horizontal lengths of the non-square transform. When theshape of the current residual block is an arbitrary shape, in operationS719, the transform kernel selector may obtain the transform kernelcandidates based on a shape of an arbitrary residual block, a scan orderof residual signal samples performed in a pre-step of thetransformation, and the intra prediction mode.

FIG. 7B is a flowchart of a process of deriving transform kernelcandidates when a current residual signal is a signal obtained by interprediction.

According to an embodiment, it may be determined whether a shape of acurrent residual block is a rectangular shape (e.g., a square shape or anon-square shape) or an arbitrary shape based on transform shapeinformation that is received as an input.

In more detail, when it is determined in operation S721 that a shape ofa current residual block is a rectangular shape based on transform shapeinformation received as an input, and when the shape is a rectangularshape, in operation S722, it may be determined whether the shape is asquare shape or a non-square shape. In contrast, when it is determinedin operation S721 based on the transform shape information received asan input that the shape of the current residual block is not arectangular shape, it may be determined that the shape of the currentresidual block is an arbitrary shape.

According to an embodiment, when it is determined based on the transformshape information that the shape of the current residual block is arectangular shape (i.e., a square shape or a non-square shape), it maybe determined whether a transform is separable or non-separable in eachof a vertical direction and a horizontal direction.

In more detail, when the shape of the current residual block is a squareshape, in operation S723, it may be determined whether the transform isseparable. When the shape of the current residual block is a non-squareshape, in operation S724, it may be determined whether the transform isseparable. For example, when the transform is separable in each of thevertical direction and the horizontal direction, transform kernelcandidates in each of the vertical direction and the horizontaldirection may be derived.

According to an embodiment, when the transform shape information andwhether the transform is separable are determined, the transform kernelcandidates may be determined based on the transform shape informationand whether the transform is separable.

In more detail, when the shape of the current residual block is a squareshape and the transform is separable, in operation S725, the transformkernel selector may obtain the transform kernel candidates that arepre-determined in each of the vertical direction and the horizontaldirection. When the shape of the current residual block is a squareshape and the transform is non-separable, in operation S726, thetransform kernel selector may obtain the pre-determined transform kernelcandidates. When the shape of the current residual block is a non-squareshape and the transform is separable, in operation S727, the transformkernel selector may obtain the transform kernel candidates in each ofthe vertical direction and the horizontal direction based on verticaland horizontal lengths of a non-square transform. When the shape of thecurrent residual block is a non-square shape and the transform isnon-separable, in operation S728, the transform kernel selector mayobtain the transform kernel candidates based on the vertical andhorizontal lengths of the non-square transform. When the shape of thecurrent residual block is an arbitrary shape, in operation S729, thetransform kernel selector may obtain the transform kernel candidatesbased on a shape of an arbitrary residual block and a scan order ofresidual samples performed in a pre-step of the transformation.

FIG. 8 is a flowchart of a method of performing transformation byadaptively selecting a transform kernel selector at an encoding end,according to an embodiment.

In operation S810, the transformer 110 may obtain a residual blockincluding a residual signal for a current coding unit.

According to an embodiment, the residual block may be generated to havethe same size and the same shape as those of the current coding unit bysubtracting a prediction block generated by inter prediction or intraprediction from a coding unit to be currently encoded.

In operation S820, the transform kernel selector 120 may obtaintransform shape information about a size or a shape of the residualblock.

According to an embodiment, the transform shape information may includeinformation about a size and a shape of a current transform. In moredetail, the transform shape information about the shape may includeinformation about whether a transform shape is a square shape, anon-square shape, or an arbitrary shape. Also, when the transform shapeis a non-square shape or an arbitrary shape, the transform shapeinformation about the shape may include information about a detailedshape (e.g., a horizontal or vertical length).

According to an embodiment, the transform kernel selector 120 may obtaininformation (i.e., intra prediction mode information) about an intraprediction mode used in intra prediction. However, when the inputresidual signal is obtained by inter prediction, the transform kernelselector 120 may not receive, as an input, the intra prediction modeinformation. Examples of the intra prediction mode may include an IntraPlanar mode, an Intra DC mode, and an Intra Angular mode. New 67prediction modes obtained by adding 32 prediction modes to existing 35prediction modes may be included in the Intra-Angular mode.

According to an embodiment, the transform kernel selector 120 mayinclude the feature that the residual signal is separable in ahorizontal direction and a vertical direction in transform kernelinformation and may send the transform kernel information to thetransformer 110.

For example, when the feature that the residual signal is separable isincluded, the transform kernel selector 120 may determine to select eachtransform kernel based on the transform shape information in each of thevertical direction and the horizontal direction of the residual signal.In contrast, when the feature that the residual signal is non-separableis included, the transform kernel information may include informationabout one transform kernel irrespective of an application direction.

In operation S830, the transform kernel selector 120 may adaptivelydetermine a transform kernel based on the transform shape information.

According to an embodiment, a transform kernel candidate deriver of thetransform kernel selector 120 may receive, as an input, the intraprediction mode information and the transform shape information, and mayderive transform kernel candidates to be applied to a current residualsignal. Also, a transform kernel determiner of the transform kernelselector 120 may receive, as an input, the transform kernel candidatesfrom the transform kernel candidate deriver, may receive, as an input, atransform kernel index from a bitstream, may determine a transformkernel to be applied to the current residual signal, and may sendtransform kernel information to the transformer 110.

When the number of the transform kernel candidates output by thetransform kernel candidate deriver is 1, the transform kernel determinermay determine the single input as a transform kernel, and may send thetransform kernel information to the transformer 110. Alternatively, whena transform is a square transform or a non-square transform and isseparable, a process of deriving transform kernel candidates anddetermining a transform kernel may be performed in each of the verticaland horizontal directions, and transform kernel information aboutvertical and horizontal transforms may be output.

In operation S840, the transformer 110 may perform transformation on theresidual signal by using the determined transform kernel.

For example, the residual block having the same size and shape as thoseof a coding unit may be split into transform units and encoding may beperformed in the transform units.

FIG. 10 illustrates that shapes into which second coding units may besplit by an image encoding apparatus are restricted when the secondcoding units having a non-square shape split and determined from a firstcoding unit 1000 satisfy a predetermined condition according to anembodiment.

According to an embodiment, an encoder may determine that the firstcoding unit 1000 having a square shape is split into second coding units1010 a, 1010 b, 1020 a, and 1020 b having a non-square shape.Accordingly, the second coding units 1010 a, 1010 b, 1020 a, and 1020 bmay be independently split. Accordingly, the encoder may determine thateach of the second coding units 1010 a, 1010 b, 1020 a, and 1020 b issplit or not split into a plurality of coding units. An operation of theimage encoding apparatus of FIG. 10 to restrict splittable shapes whensecond coding units having a non-square shape satisfy a predeterminedcondition may be opposite to an operation of an image decoding apparatusto be described below with reference to FIG. 10, and thus a detailedexplanation thereof will not be given.

FIG. 11 illustrates a process by which an image encoding apparatussplits a coding unit having a square shape when slit shape informationis unable to indicate that a coding unit is split into four squarecoding units. An operation of the image encoding apparatus in this casemay be opposite to an operation of an image decoding apparatus to bedescribed below with reference to FIG. 11, and thus a detailedexplanation thereof will not be given.

FIG. 12 illustrates that an order of processing a plurality of codingunits may vary according to a process of splitting a coding unitaccording to an embodiment.

According to an embodiment, an encoder may split a first coding unit1200 having a square shape in at least one of a horizontal direction anda vertical direction. According to an embodiment, a bitstream generatormay generate a bitstream including block shape information indicatingthat the first coding unit 120 has a square shape and split shapeinformation indicating that the first coding unit 1200 is split in atleast one of the horizontal direction and the vertical direction.

According to an embodiment, the encoder may determine second codingunits (e.g., 1210 a, 1210 b, 1220 a, 1220 b, 1230 a, 1230 b, 1230 c, and1230 d) by splitting the first coding unit 1200. Referring to FIG. 12,the second coding units 1210 a, 1210 b, 1220 a, and 1220 b having anon-square shape determined by splitting the first coding unit 1200 inthe horizontal direction or the vertical direction may be independentlysplit. For example, the encoder may determine third coding units 1216 athrough 1216 d by respectively splitting, in the horizontal direction,the second coding units 1210 a and 1210 b generated as the first codingunit 1200 is split in the vertical direction, and may determine thirdcoding units 1226 a through 1226 d by respectively splitting, in thehorizontal direction, the second coding units 1220 a and 1220 bgenerated as the first coding unit 1200 is split in the horizontaldirection. An operation of an image encoding apparatus related to FIG.10 may be opposite to an operation of an image decoding apparatus to bedescribed below with reference to FIG. 10, and thus a detailedexplanation thereof will not be given.

FIG. 13 illustrates a process of determining a depth of a coding unitaccording to a change in a shape and a size of the coding unit when aplurality of coding units are determined as the coding unit isrecursively split according to an embodiment. A process by which anencoder of an image encoding apparatus determines a depth of a codingunit may be opposite to a process by which a decoder of an imagedecoding apparatus determines a depth of a coding unit to be describedbelow with reference to FIG. 13, and thus a detailed explanation thereofwill not be given.

According to an embodiment, the image encoding apparatus may determinewhether a coding unit is split into a specific split shape based on avalue of an index for distinguishing a plurality of coding units splitand determined from a current coding unit. Referring to FIG. 14, theimage encoding apparatus may determine an even number of coding units1412 a and 1412 b or an odd number of coding units 1414 a, 1414 b, and1414 c by splitting a first coding unit 1410 having a long rectangularshape in which a height is greater than a width. The image encodingapparatus may use a part index (PID) indicating each coding unit todistinguish each of the plurality of coding units. According to anembodiment, the PID may be obtained from a sample (e.g., an upper leftsample) at a predetermined location of each coding unit. An operation ofthe image encoding apparatus related to FIG. 14 may be opposite to anoperation of an image decoding apparatus to be described below withreference to FIG. 14, and thus a detailed explanation thereof will notbe given.

FIG. 15 illustrates that a plurality of coding units are determinedaccording to a plurality of predetermined data units included in apicture according to an embodiment. According to an embodiment, anencoder may use a reference coding unit as a predetermined data unitfrom which a coding unit starts to be recursively split. An operation bywhich an image encoding apparatus uses the reference coding unit relatedto FIG. 15 may be opposite to an operation by which an image decodingapparatus uses the reference coding unit to be described below withreference to FIG. 15, and thus a detailed explanation thereof will notbe given.

According to an embodiment, a bitstream generator of the image encodingapparatus may generate, for various data units, a bitstream including atleast one of information about a shape of the reference coding unit andinformation about a size of the reference coding unit. A process ofdetermining at least one coding unit included in a reference coding unit1500 having a square shape has been described above in a process ofsplitting a current coding unit, and a process of determining at leastone coding unit included in the reference coding unit 1500 having anon-square shape has been described above in the process of splittingthe current coding unit, and thus a detailed explanation thereof willnot be given.

According to an embodiment, in order to determine a size and a shape ofa reference coding unit according to some pre-determined data unitsbased on a predetermined condition, the encoder may use a PID foridentifying the size and the shape of the reference coding unit. Thatis, for each data unit satisfying a predetermined condition (e.g., adata unit having a size equal to or less than a slice) from among thevarious data units (e.g., a sequence, a picture, a slice, a slicesegment, and a largest coding unit), the bitstream generator maygenerate a bitstream including the PID for identifying the size and theshape of the reference coding unit. The encoder may determine the sizeand the shape of the reference data unit for each data unit satisfyingthe predetermined condition by using the PID. According to anembodiment, at least one of the size and the shape of the referencecoding unit related to the PID indicating the size and the shape of thereference coding unit may be pre-determined. That is, the encoder maydetermine at least one of the size and the shape of the reference codingunit included in a data unit that becomes a criterion for obtaining thePID by selecting at least one of the pre-determined size and shape ofthe reference coding unit according to the PID. An operation of theencoder using the PID for identifying the size and the shape of thereference coding unit may be similar to an operation of a decoderdescribed above, and thus a detailed explanation thereof will not begiven.

FIG. 16 illustrates a processing block that becomes a criterion fordetermining a determining order of reference coding units included in apicture 1600 according to an embodiment.

According to an embodiment, an encoder may obtain information about asize of a processing block and may determine a size of at least oneprocessing block included in an image. The encoder may determine thesize of the at least one processing block included in the image, and abitstream generator may generate a bitstream including information abouta size of a processing block. The size of the processing block may be apredetermined size of a data unit indicated by the information about asize of a processing block.

According to an embodiment, the bitstream generator of an image encodingapparatus may generate the bitstream including the information about asize of a processing block according to predetermined data units. Forexample, the bitstream generator may generate the bitstream includingthe information about a size of a processing block according to dataunits such as images, sequences, pictures, slices, and slice segments.That is, the bitstream generator may generate the bitstream includingthe information about a size of a processing block according to suchseveral data units, and the encoder may determine the size of at leastone processing block splitting the picture by using the informationabout a size of a processing block, wherein the size of the processingblock may be an integer times a size of a reference coding unit.

According to an embodiment, the encoder may determine sizes ofprocessing blocks 1602 and 1612 included in the picture 1600. Forexample, the encoder may determine a size of a processing block based oninformation about a size of a processing block. Referring to FIG. 16,the encoder may determine a horizontal size of each of the processingblocks 1602 and 1612 to be 4 times a horizontal size of a referencecoding unit, and a vertical size of each of the processing blocks 1602and 1612 to be 4 times a vertical size of the reference coding unitaccording to an embodiment. The encoder may determine a determiningorder of at least one reference coding unit in at least one processingblock. An operation of the encoder related to the processing block maybe similar to an operation of a decoder described above with referenceto FIG. 16, and thus a detailed explanation thereof will not be given.

According to an embodiment, the bitstream generator of the imageencoding apparatus may generate a bitstream including block shapeinformation indicating a shape of a current coding unit or split shapeinformation indicating a method of splitting the current coding unit.The block shape information or the split shape information may beincluded in a bitstream related to various data units. For example, thebitstream generator of the image encoding apparatus may use the blockshape information or the split shape information included in a sequenceparameter set, a picture parameter set, a video parameter set, a sliceheader, and a slice segment header. Furthermore, the bitstream generatorof the image encoding apparatus may generate the bitstream includingsyntax indicating the block shape information or the split shapeinformation according to largest coding units, reference coding units,and processing blocks.

According to an embodiment, the encoder may differently determine typesof split shapes into which a coding unit may be split according topredetermined data units. The encoder of the image encoding apparatusmay differently determine combinations of shapes into which a codingunit may be split according to predetermined data unit (e.g., sequences,pictures, and slices).

FIG. 17 illustrates coding units that may be determined for eachpicture, when combinations of shapes into a coding unit may be split aredifferent among pictures according to an embodiment.

Referring to FIG. 17, an encoder may differently determine a combinationof split shapes into which a coding unit may be split for each picture.For example, the encoder may decode an image by using a picture 1700that may be split into four coding units, a picture 1710 that may besplit into two or four coding units, and a picture 1720 that may besplit into two, three, or four coding units from among one or morepictures included in the image. The encoder may split the picture 1700into four square coding units. The encoder may split the picture 1710into two or four coding units. The encoder may split the picture 1720into two, three, or four coding units. The combination of split shapesis merely an embodiment for describing an operation of an image encodingapparatus, and thus the combination of split shapes should not beinterpreted as being limited to the embodiment and various combinationsof split shapes may be used according to predetermined data units.

According to an embodiment, the encoder of the image encoding apparatusmay determine a combination of split shapes into which a coding unit maybe split according to predetermined data units by using an indexindicating a combination of split shape information, and thus may usethe different combination of split shapes according to predetermineddata units. Furthermore, a bitstream generator of the image encodingapparatus may generate a bitstream including the index indicating thecombination of the split shape information according to predetermineddata units (e.g., sequences, pictures, and slices). For example, thebitstream generator may generate the bitstream including the indexindicating the combination of the split shape information in a sequenceparameter set, a picture parameter set, or a slice.

FIGS. 18 and 19 illustrate various shapes of a coding unit that may bedetermined based on split shape information that may be represented as abinary code according to an embodiment.

According to an embodiment, an encoder of an image encoding apparatusmay split a coding unit into various shapes, and a bitstream generatormay generate a bitstream including block shape information and splitshape information. Shapes into which the coding unit may be split maycorrespond to various shapes including shapes described with referenceto the above embodiments. Referring to FIG. 18, the encoder may split acoding unit having a square shape in at least one of a horizontaldirection and a vertical direction and may split a coding unit having anon-square shape in the horizontal direction or the vertical directionbased on the split shape information. Characteristics of a binary codeof the split shape information that may be used by the image encodingapparatus may correspond to characteristics of an image decodingapparatus to be described below with reference to FIGS. 18 and 19, andthus a detailed explanation thereof will not be given.

The image encoding apparatus according to an embodiment may generateprediction data by performing inter prediction or intra prediction on acoding unit, may generate residual data by performing transformation ona transform unit included in a current coding unit, and may encode thecurrent coding unit by using the generated prediction data and thegenerated residual data.

A prediction mode of a coding unit according to an embodiment may be atleast one of an intra mode, an inter mode, and a skip mode. According toan embodiment, a prediction mode having a smallest error may be selectedby independently performing prediction for each coding unit.

When a coding unit having a 2N×2N shape according to an embodiment issplit into two coding units having a 2N×N shape or a N×2N shape, intermode prediction and intra mode prediction may be separately performed oneach coding unit. Also, according to an embodiment, the encoder of theimage encoding apparatus may encode a coding unit by using a coding unit(CU) skip mode not only when the coding unit has a square shape but alsowhen the coding unit has a non-square shape. Since an image may bedecoded by using a CU skip mode not only for a coding unit having asquare shape but also for a coding unit having a non-square shape thatmay be determined based on at least one of block shape information andsplit shape information, a skip mode may be more adaptively used,thereby improving image encoding/decoding efficiency. Characteristics ofthe image encoding apparatus using a skip mode in a coding unit havingsuch a non-square shape may be similar to those described with referenceto the use of a skip mode of the image encoding apparatus, and thus adetailed explanation thereof will not be given.

FIG. 22 illustrates a process of performing a merge operation or a splitoperation on coding units determined according to a predeterminedencoding method, according to an embodiment.

According to an embodiment, an image encoding apparatus may determinecoding units for splitting a picture by using the predetermined encodingmethod. For example, the image encoding apparatus may determine a codingunit of a current depth or may split the coding unit into four codingunits of a lower depth based on split information of the coding unit. Asdescribed above, the image encoding apparatus may determine a codingunit by using block shape information indicating that a current codingunit always has a square shape, and split shape information indicatingthat the current coding unit is not split or split into four squarecoding units. Referring to FIG. 22, pictures 2200 and 2220 may be splitaccording to square coding units determined according to thepredetermined encoding method.

However, when the above-described predetermined decoding unit is used,since whether a current coding unit is split is determined according towhether it is suitable to represent a relatively small object includedin the current coding unit, it may be impossible to encode a largeobject and a small object in a picture through one coding unit. The term‘object’ that is a set of samples included in a picture may refer to aregion of samples distinguished from other regions as the samples havesimilar sample values. Referring to FIG. 22, the image encodingapparatus may determine a coding unit for decoding a small object 2221by splitting a first coding unit 2222 into four coding units of a lowerdepth in order to reconstruct the small object 2221. However, since alarge object 2223 is not included in the first coding unit 2222 that isa current coding unit, it is not suitable to decode the large object2223 by using the current coding unit 2222, and furthermore, since thecurrent coding unit 2222 is split in order to decode the small object2221, an unnecessary process of splitting a coding unit has to beperformed in order to decode the large object 2223 inefficiently. Thatis, image encoding may be efficiently performed if the image encodingapparatus may use one coding unit in order to encode a partcorresponding to the large object 2223.

According to an embodiment, an encoder of the image encoding apparatusmay split a current coding unit by using at least one of block shapeinformation and split shape information, the block shape information maybe pre-determined to use only a square shape, and the split shapeinformation may be pre-determined to indicate whether a coding unit isnot split or split into four square coding units. Such a process maycorrespond to a process of determining a coding unit used in thepredetermined encoding method described with reference to variousembodiments. In this case, in order to merge coding units determined byusing the predetermined encoding method or to split the determinedcoding units, the encoder may use a sample value included in a picture.For example, the encoder may detect various objects included in apicture by examining parts having similar sample values, and may performa merge/split operation on coding units based on parts corresponding tothe detected objects.

Referring to FIG. 22, according to an embodiment, the encoder maydetermine a plurality of coding units for splitting the picture 2200 byusing the predetermined encoding method. However, although there is apart 2201 having a similar sample value included in the picture 2200, aprocess of splitting a similar region into a plurality of coding units,instead of one coding unit, may be performed. In this case, even whencoding units are determined by using the predetermined encoding method,the coding units may be merged into one coding unit 2202 and may beencoded as one coding unit. Referring to FIG. 22, according to anotherembodiment, the encoder may split the coding unit 2222 for encoding thesmall object 2221 into four coding units by using the predeterminedencoding method. Since the large object 2223 may not be included in allof the four coding units, the encoder may perform a merge operation 2225by merging the coding units into one coding unit including a part havinga similar sample value.

According to an embodiment, the encoder may determine a coding unit byusing a predetermined encoding method of not splitting or splitting acoding unit into four coding units by using split information of thecoding unit, and then may split again the coding unit in considerationof sample values of samples included in a picture. That is, in order todetermine a coding unit for each object, the encoder 130 may perform notonly a merge operation on coding units but also a split operation on adetermined coding unit. Referring to FIG. 22, since the encoder 130 maymerge coding units for the large object 2223, and then may perform asplit operation 2226 again on the merged coding units for the largeobject 2223 in order to determine an optimized coding unit for the largeobject 2223. That is, the encoder may determine a part not including thelarge object 2223 as a coding unit 2227 separate from the large object2223 through the split operation 2226.

When a merge operation or a split operation is performed on coding unitsdetermined according to a predetermined encoding method through anoperation of the image encoding apparatus and then a bitstream for animage is generated, an image decoding apparatus may obtain the bitstreamand then may decode the image by performing an image decoding method inreverse order to an order in which the image encoding method isperformed.

FIG. 23 illustrates an index according to a Z-scan order of a codingunit, according to an embodiment.

An encoder of an image encoding apparatus according to an embodiment mayscan lower data units included in an upper data unit according to aZ-scan order. Also, the image encoding apparatus according to anembodiment may sequentially access data according to a Z-scan index in acoding unit included in a processing block or a largest coding unit. Inthis case, coding units having a square shape and coding units having anon-square shape may exist together in a reference coding unit.Characteristics of an index according to a Z-scan order of a coding unitof the image encoding apparatus may be similar to characteristics of animage decoding apparatus to be described below with reference to FIG.23, and thus a detailed explanation thereof will not be given.

The above-described various embodiments are for describing an operationrelated to an image encoding method performed by the image encodingapparatus. An operation of the image decoding apparatus that performs animage decoding method in reverse order to an order in which the imageencoding method is performed will now be described with reference tovarious embodiments.

FIG. 2 is a block diagram of a decoding apparatus including an extractor210, a transform kernel selector 230 that adaptively selects a transformkernel based on a transform shape, a transformer 220, and a decoder 240,according to an embodiment.

Referring to FIG. 2, the extractor 210 may obtain data of a currentcoding unit and transform shape information about a size or a shape of aresidual block for the current coding unit from a parsed bitstream.

According to an embodiment, when the extractor 210 obtains currentencoded data, the transformer 220 may perform transformation. Also, thetransform kernel selector 230 may determine transform kernel informationabout a transform kernel to be applied and may apply the determinedtransform kernel information as an input to the transformer 220. Forexample, the encoded data may include information about a transformcoefficient obtained from a residual signal.

According to an embodiment, the transform kernel selector 230 mayreceive the transform shape information as a basic input. For example,the transform shape information may include information about a size anda shape of a current transform. In more detail, the transform shapeinformation about the shape may include information about whether atransform shape is a square shape, a non-square shape, or an arbitraryshape. Also, when the transform shape is a non-square shape or anarbitrary shape, the transform shape information about the shape mayinclude information about a detailed shape (e.g., a horizontal orvertical length). The transform shape information about the size mayinclude information about vertical and horizontal lengths of a squaretransform, a non-square transform, or an arbitrary transform. Also, whenthe transform shape is an arbitrary shape, the transform shapeinformation about the size may further include information about adiagonal length.

According to an embodiment, the transform kernel selector 230 may obtaininformation indicating whether the residual signal included in the dataof the coding unit obtained from the bitstream is a signal obtained byperforming intra prediction. For example, the transform kernel selector230 may obtain prediction information indicating whether the residualsignal included in the data of the coding unit obtained from thebitstream is a signal obtained by performing intra prediction. Theprediction information may indicate whether the residual signal obtainedfrom the bitstream is a signal obtained by performing intra predictionor a signal obtained by performing inter prediction.

According to an embodiment, when the residual signal obtained from thebitstream is obtained by intra prediction, the transform kernel selector230 may obtain information (i.e., intra prediction mode information)about an intra prediction mode used in the intra prediction. Forexample, the intra prediction mode may indicate an index in an Intra DCmode, an Intra Planar mode, and an Intra Angular mode. When the residualsignal obtained from the bitstream is obtained by inter prediction, thetransform kernel selector 230 may not receive the intra prediction modeinformation as an input.

Examples of the intra prediction mode for a luminance component mayinclude the Intra Planar mode, the Intra DC mode, and the Intra Angularmode. In more detail, in the Intra Planar mode, a prediction value maybe generated by averaging values obtained by performing linearinterpolation (interpolation using a weight according to a distance) inhorizontal and vertical directions on values obtained by copyingreference pixels. Also, in the Intra DC mode, an average value ofneighboring pixels of a current block may be used as a prediction value.Prediction in the Intra DC mode may be performed by filtering sampleslocated at a boundary of a prediction block in order to removediscontinuity between a prediction sample and reference samples, withoutusing an average value for a block to be predicted as the predictionsample. Also, in the Intra Angular mode, a prediction sample may beobtained in consideration of directionality when the prediction sampleis calculated from reference samples. Directionality according to eachmode in the Intra Angular mode will be described below with reference toFIG. 6.

Also, examples of the intra prediction mode for a chrominance componentmay include the Intra DC mode, an Intra Vertical mode, anIntra-Horizontal mode, and an Intra DM mode. The modes other than theIntra DM mode may generate a prediction sample by using the same processas the method described for the luminance component. In the Intra DMmode, a mode of a chrominance component may be used as the same mode asthat of a luminance component by using the feature that the luminancecomponent and the chrominance component are similar to each other.

According to an embodiment, the transformer 220 may apply transformationto the original residual signal based on the transform kernelinformation determined and transmitted as an input by the transformkernel selector 230, and then may output a reconstructed transformcoefficient as a result of the transformation.

For example, the transform kernel selector 230 may adaptively select atransform kernel based on at least one of the transform shapeinformation and the intra prediction mode information. For example, thetransform kernel selector 230 may send the transform kernel informationabout the adaptively selected transform kernel to the transformer 220.In this case, the transformer 220 may perform transformation on theoriginal residual signal by applying the selected transform kernel basedon the received transform kernel information. A kernel that is a DCT orapproximates a DCT to an integer transform may be used as the transformkernel, and when the residual signal is a signal having a size of 4×4obtained by intra prediction, a kernel obtained by approximating a DSTmay be used. For example, types of the transform kernel may includetransform kernels obtained by integerizing DCT-5, DCT-8, DST-1, andDST-7 transforms. Also, when the residual signal is a signal to whichintra prediction is applied, types of the transform kernel may include atransform kernel obtained by offline training for each intra predictionmode and transform shapes. Also, when the residual signal is a signal towhich inter prediction is applied, types of the transform kernel mayinclude a transform kernel obtained by offline training according toeach transform shape besides DCT and DST transforms. The types of thetransform kernel are merely examples, and the present disclosure is notlimited thereto.

For example, the transform kernel selector 230 may select a kernel to beused for a current transform unit from among a plurality of pre-definedcandidate transform kernels, may apply the selected kernel, and mayadditionally transmit information about the selected kernel. In thiscase, the set of candidate kernels may be fixed in a coding unit towhich inter prediction is applied, and may vary according to aprediction mode in a coding unit to which intra prediction is applied.Also, for example, the transformer 220 may perform secondarytransformation where a transform is applied again to a transformcoefficient obtained after primary transformation. In more detail, ROTmay involve splitting a transform coefficient into 4×4 units, selectingone from among pre-determined secondary transformations, and applyingthe selected secondary transformation. Also, in NSST that operates likethe ROT, a transform kernel may be non-separable and a secondarytransform kernel candidate to be applied may vary based on an intraprediction mode.

According to an embodiment, a decoder 240 may perform decoding based onthe transform coefficient generated by the transformer 220. For example,when a reconstructed differential coefficient signal is generated byapplying an inverse transform, the decoder 240 may decode an image byadding a reconstructed differential coefficient value to a predictionblock. In this case, the derived prediction block may be the same whenthe residual coefficient is obtained and the image is decoded.

FIG. 3 illustrates a transform shape applicable during transformation,according to an embodiment.

According to an embodiment, an image decoding apparatus may split acoding unit into various shapes by using block shape information andsplit shape information obtained by a bitstream obtainer. Shapes intowhich the coding unit may be split may correspond to various shapesincluding shapes described with reference to the above embodiments.

According to an embodiment, a shape of a residual block may be a squareshape obtained by splitting a coding unit having a square shape in atleast one of a horizontal direction and a vertical direction, or may bea non-square shape obtained by splitting a coding unit having anon-square shape in the horizontal direction or the vertical direction.

According to an embodiment, transform shape information may berepresented as a two-digit binary code, and a binary code may beassigned to each transform shape. For example, when a coding unit is notsplit, the transform shape information may be represented as (00)b; whena coding unit is split in the horizontal direction and the verticaldirection, the transform shape information may be represented as (01)b;when a coding unit is split in the horizontal direction, the transformshape information may be represented as (10)b; and when a coding unit issplit in the vertical direction, the transform shape information may berepresented as (11)b.

Also, for example, a coding unit may be split into two coding units, andin this case, the transform shape information may be represented as(10)b. Also, a coding unit may be split into three coding units, and inthis case, the transform shape information may be represented as (11)b.Also, it may be determined that a coding unit is not split, and in thiscase, the transform shape information may be represented as (0)b. Inorder to use a binary code indicating the transform shape information,VLC, instead of FLC, may be used.

FIG. 4 illustrates that a transform kernel is assigned according towhether separation is vertical separation or horizontal separation,according to an embodiment.

According to an embodiment, the transform kernel selector 230 maydetermine a shape of a residual block (i.e., whether the shape of theresidual block is a square shape or a non-square shape), and maydetermine whether transformation may be performed by separating aresidual signal in a vertical direction and a horizontal direction. Forexample, the transform kernel selector 230 may include the feature thatthe residual signal is separable in transform kernel information and maysend the transform kernel information to a transformer.

According to an embodiment, when the feature the residual signal isseparable is included, the transform kernel selector 230 may determineto select each transform kernel based on transform shape information ofthe residual signal in each of the vertical direction and the horizontaldirection.

For example, when the transform kernel information about the residualblock 410 includes the feature that the shape of the residual block is asquare shape or a non-square shape and is separable, the transformkernel information may include information about a transform kernel tobe applied in each of the vertical and horizontal directions. Incontrast, when the shape of the residual block is a square shape or anon-square shape and is non-separable or when a transform is anarbitrary transform, like in the residual block 420, the transformkernel information may include information about one transform kernelirrespective of an application direction.

FIG. 5 is a block diagram of a transform kernel selector including thetransform kernel candidate deriver 510 and the transform kerneldeterminer 520, according to an embodiment.

According to an embodiment, the transform kernel selector may includethe transform kernel candidate deriver 510 and the transform kerneldeterminer 520. The transform kernel candidate deriver 510 may receive,as an input, transform shape information and intra prediction modeinformation from a bitstream, and may derive transform kernel candidatesto be applied to a current residual signal based on at least one of thetransform shape information and the intra prediction mode information.The intra prediction mode information may be sent to the transformkernel candidate deriver 510 only when the current residual signal isobtained by intra prediction.

According to an embodiment, the transform kernel candidates may includeone or more sets of transform kernel candidates. For example, transformkernels obtained by integerizing DCT-5, DCT-8, DST-1, and DST-7transforms may be included in the transform kernel candidates. Also,when the residual signal is a residual signal to which intra predictionis applied, a transform kernel obtained by offline training for eachintra prediction mode and transform shapes may be included in thetransform kernel candidates. Also, when the residual signal is aresidual signal to which inter prediction is applied, a transform kernelobtained by offline training according to each transform shape besidesDCT and DST transforms may be included in types of the transform kernelcandidates. The transform kernel candidates may be merely examples, andthe present disclosure is not limited thereto.

According to an embodiment, the number of the transform kernelcandidates may be determined based on at least one of the transformshape information and the intra prediction mode information. Forexample, the number of the transform kernel candidates may be determinedaccording to a vertical or horizontal length when a transform shape is asquare shape, a non-square shape, or an arbitrary shape. Also, forexample, the number of the transform kernel candidates may be determinedaccording to whether an intra prediction mode is a Planar mode or a DCmode without directionality or has directionality.

The transform kernel determiner 520 may receive, as an input, thetransform kernel candidates from the transform kernel candidate deriver510, may receive, as an input, a transform kernel index from thebitstream, may determine a transform kernel to be applied to the currentresidual signal, and may send transform kernel information to atransformer.

According to an embodiment, the transform kernel index may include indexinformation about a kernel to be applied to the current residual signalfrom among the plurality of transform kernel candidates. For example,the transform kernel index may be applied, as an input, only when thetransform kernel candidates include a plurality of sets of transformkernel candidates, and the transform kernel index may be included in thebitstream as described above. For example, when the number of thetransform kernel candidates output by the transform kernel candidatederiver 510 is 1, the transform kernel determiner 520 may determine thesingle input as a transform kernel, and may send transform kernelinformation to the transformer. For example, when a transform is asquare transform or a non-square transform and is separable, a processof deriving transform kernel candidates and determining a transformkernel may be performed in each of a vertical direction and a horizontaldirection, and transform kernel information about vertical andhorizontal transforms may be output.

FIG. 6 illustrates information about an intra prediction mode accordingto an embodiment.

According to an embodiment, the transform kernel selector 230 may obtainintra prediction mode information from a bitstream, and new 67prediction modes obtained by adding 32 prediction modes 620 to existing35 prediction modes 610 may be included in the intra prediction mode.

For example, when intra prediction is performed by using both the leftand top data units 630 or the right and bottom data units 640 accordingto the intra prediction mode, the transform kernel selector 230 mayobtain intra prediction mode information used in each intra prediction,and may select a transform kernel based on each obtained intraprediction mode information.

FIGS. 7A and 7B are flowcharts of a process of deriving transform kernelcandidates according to an embodiment.

FIG. 7A is a flowchart of a process of deriving transform kernelcandidates when a current residual signal is a signal obtained by intraprediction.

According to an embodiment, encoded data of a current coding unit andtransform shape information about a size or a shape of a residual blockincluding a residual signal for the current coding unit may be obtainedfrom a bitstream.

According to an embodiment, it may be determined whether a shape of acurrent residual block is a rectangular shape (e.g., a square shape or anon-square shape) or an arbitrary shape based on the transform shapeinformation obtained from the bitstream.

In more detail, in operation S711, it may be determined whether a shapeof a current residual block is a rectangular shape based on transformshape information obtained from a bitstream, and when the shape is arectangular shape, in operation S712, it may be determined that theshape is a square shape or a non-square shape. In contrast, when it isdetermined in operation S711 based on the transform shape informationobtained from the bitstream that the shape of the current residual blockis not a rectangular shape, it may be determined that the shape of thecurrent residual block is an arbitrary shape.

According to an embodiment, when it is determined based on the transformshape information that the shape of the current residual block is arectangular shape (i.e., a square shape or a non-square shape), it maybe determined whether a transform is separable or non-separable in eachof a vertical direction and a horizontal direction.

In more detail, when the shape of the current residual block is a squareshape, in operation S713, it may be determined whether the transform isseparable. When the shape of the current residual block is a non-squareshape, in operation S714, it may be determined that the transform isseparable. For example, when the transform is separable in each of thevertical direction and the horizontal direction, transform kernelcandidates in each of the vertical direction and the horizontaldirection may be derived.

According to an embodiment, when the transform shape information andwhether the transform is separable are determined, the transform kernelcandidates may be determined based on the transform shape informationand whether the transform is separable.

In more detail, when the shape of the current residual block is a squareshape and the transform is separable, in operation S715, the transformkernel selector 230 may obtain the transform kernel candidates in eachof the vertical direction and the horizontal direction based on an intraprediction mode. When the shape of the current residual block is asquare shape and the transform is non-separable, in operation S716, thetransform kernel selector 230 may obtain the transform kernel candidatesbased on the intra prediction mode. When the shape of the currentresidual block is a non-square shape and the transform is separable, inoperation S717, the transform kernel selector 230 may obtain thetransform kernel candidates in each of the vertical direction and thehorizontal direction based on the intra prediction mode and vertical andhorizontal lengths of a non-square transform. When the shape of thecurrent residual block is a non-square shape and the transform isnon-separable, in operation S718, the transform kernel selector 230 mayobtain the transform kernel candidates based on the intra predictionmode and the vertical and horizontal lengths of the non-squaretransform. When the shape of the current residual block is an arbitraryshape, in operation S719, the transform kernel selector 230 may obtainthe transform kernel candidates based on a shape of an arbitraryresidual block, a scan order of residual signal samples performed in apre-step of the transformation, and the intra prediction mode.

FIG. 7B is a flowchart of a process of deriving transform kernelcandidates when a current residual signal is a signal obtained by interprediction.

According to an embodiment, encoded data of a current coding unit andtransform shape information about a size or a shape of a residual blockincluding a residual signal for the current coding unit may be obtainedfrom a bitstream.

According to an embodiment, it may be determined whether a shape of acurrent residual block is a rectangular shape (e.g., a square shape or anon-square shape) or an arbitrary shape based on the transform shapeinformation obtained from the bitstream.

In more detail, when it is determined in operation S721 that a shape ofa current residual block is a rectangular shape based on transform shapeinformation obtained from a bitstream, and when the shape is arectangular shape, in operation S722, it may be determined whether theshape is a square shape or a non-square shape. In contrast, when it isdetermined in operation S721 based on the transform shape informationobtained from the bitstream that the shape of the current residual blockis not a rectangular shape, it may be determined that the shape of thecurrent residual block is an arbitrary shape.

According to an embodiment, when it is determined based on the transformshape information that the shape of the current residual block is arectangular shape (i.e., a square shape or a non-square shape), it maybe determined whether a transform is separable or non-separable in eachof a vertical direction and a horizontal direction.

In more detail, when the shape of the current residual block is a squareshape, in operation S723, it may be determined whether the transform isseparable. When the shape of the current residual block is a non-squareshape, in operation S724, it may be determined whether the transform isseparable. For example, when the transform is separable in each of thevertical direction and the horizontal direction, transform kernelcandidates in each of the vertical direction and the horizontaldirection may be derived.

According to an embodiment, when the transform shape information andwhether the transform is separable are determined, the transform kernelcandidates may be determined based on the transform shape informationand whether the transform is separable.

In more detail, when the shape of the current residual block is a squareshape and the transform is separable, in operation S725, the transformkernel selector 230 may obtain the transform kernel candidates that arepre-determined in each of the vertical direction and the horizontaldirection. When the shape of the current residual block is a squareshape and the transform is non-separable, in operation S716, thetransform kernel selector 230 may obtain the pre-determined transformkernel candidates. When the shape of the current residual block is anon-square shape and the transform is separable, in operation S717, thetransform kernel selector 230 may obtain the transform kernel candidatesin each of the vertical direction and the horizontal direction based onvertical and horizontal lengths of a non-square transform. When theshape of the current residual block is a non-square shape and thetransform is non-separable, in operation S718, the transform kernelselector 230 may obtain the transform kernel candidates based on thevertical and horizontal lengths of the non-square transform. When theshape of the current residual block is an arbitrary shape, in operationS719, the transform kernel selector 230 may obtain the transform kernelcandidates based on a shape of an arbitrary residual block and a scanorder of residual samples performed in a pre-step of the transformation.

FIG. 9 is a flowchart of a method of performing transformation byadaptively selecting the transform kernel selector 230 at a decodingend, according to an embodiment.

In operation S910, the extractor 210 may extract data of a currentcoding unit from among coding units that are data units for encoding acurrent picture of an encoded video and transform shape informationabout a size or a shape of a residual block for the current coding unitfrom a parsed bitstream.

In operation S920, the transform kernel selector 230 may adaptivelydetermine a transform kernel based on the transform shape informationobtained from the bitstream in order to decode encoded data.

According to an embodiment, the transform shape information may includeinformation about a size and a shape of a current transform. In moredetail, the transform shape information about the shape may includeinformation about whether a transform shape is a square shape, anon-square shape, or an arbitrary shape. Also, when the transform shapeis a non-square shape or an arbitrary shape, the transform shapeinformation about the shape may include information about a detailedshape (e.g., a horizontal or vertical length).

According to an embodiment, the transform kernel selector 230 may obtaininformation (i.e., intra prediction mode information) about an intraprediction mode used in intra prediction. However, when an inputresidual signal is obtained by inter prediction, the transform kernelselector 230 may not receive the intra prediction mode information as aninput. Examples of the intra prediction mode may include an Intra Planarmode, an Intra DC mode, and an Intra Angular mode. New 67 predictionmodes obtained by adding 32 prediction modes to existing 35 predictionmodes may be included in the Intra-Angular mode.

According to an embodiment, the transform kernel selector 230 mayinclude the feature that the residual signal is separable in ahorizontal direction and a vertical direction in transform kernelinformation and may send the transform kernel information to thetransformer 220.

For example, when the feature that the residual signal is separable isincluded, the transform kernel selector 230 may determine to select eachtransform kernel based on the transform shape information in each of thevertical direction and the horizontal direction of the residual signal.In contrast, when the feature that the residual signal is non-separableis included, the transform kernel information may include informationabout one transform kernel irrespective of an application direction.

According to an embodiment, a transform kernel candidate deriver of thetransform kernel selector 230 may obtain the intra prediction modeinformation and the transform shape information from the bitstream, andmay derive transform kernel candidates to be applied to a currentresidual signal. Also, a transform kernel determiner of the transformkernel selector 230 may receive, as an input, the transform kernelcandidates from the transform kernel candidate deriver, may receive, asan input, a transform kernel index from the bitstream, may determine atransform kernel to be applied to the current residual signal, and maysend the transform kernel information to the transformer 220.

When the number of the transform kernel candidates output by thetransform kernel candidate deriver is 1, the transform kernel determinermay determine the single input as a transform kernel, and may send thetransform kernel information to the transformer 220. Alternatively, whena transform is a square transform or a non-square transform and isseparable, a process of deriving transform kernel candidates anddetermining a transform kernel may be performed in each of the verticaland horizontal directions, and the transform kernel information aboutvertical and horizontal transforms may be output.

In operation S930, the transformer 220 may generate a residual signalfor the current coding unit by performing transformation on the currentcoding unit by using the determined transform kernel.

According to an embodiment, the transformer 220 may generate areconstructed residual signal by performing de-quantization and inversetransformation.

In operation S940, the decoder 240 may perform decoding based on thegenerated residual signal.

According to an embodiment, the decoder 240 may reconstruct the currentcoding unit by using prediction data and the generated residual signal.

FIG. 10 illustrates that shapes into which second coding units may besplit by an image decoding apparatus are restricted when the secondcoding units having a non-square shape split and determined from thefirst coding unit 1000 satisfy a predetermined condition, according toan embodiment.

According to an embodiment, the decoder 240 may determine that the firstcoding unit 1000 having a square shape is split into the second codingunits 1010 a, 1010 b, 1020 a, and 1020 b having a non-square shape basedon at least one of block shape information and split shape informationobtained by a bitstream obtainer. The second coding units 1010 a, 1010b, 1020 a, and 1020 b may be independently split. Accordingly, thedecoder 240 may determine that each of the second coding units 1010 a,1010 b, 1020 a, and 1020 b is slit or not split into a plurality ofcoding units based on at least one of block shape information and splitshape information related to each of the second coding units 1010 a,1010 b, 1020 a, and 1020 b. According to an embodiment, the decoder 240may determine third coding units 1012 a and 1012 b by splitting, in ahorizontal direction, the second coding unit 1010 a at the left having anon-square shape, which is determined when the first coding unit 1000 issplit in a vertical direction. However, when the second coding unit 1010a at the left is split in the horizontal direction, the decoder 240 mayset a limit so that the second coding unit 1010 b at the right is notsplit in the same direction, i.e., the horizontal direction, as thedirection in which the second coding unit 1010 a at the left is split.When third coding units 1014 a and 1014 b are determined when the secondcoding unit 1010 b at the right is split in the same direction, thethird coding units 1012 a, 1012 b, 1014 a, and 1014 b may be determinedwhen the second coding unit 1010 a at the left and the second codingunit 1010 b at the right are each independently split in the horizontaldirection. However, this is the same result as that obtained when thedecoder 240 splits the first coding unit 1000 into four second codingunits 1030 a, 1030 b, 1030 c, and 1030 d having a square shape based onat least one of block shape information and split shape information, andthus may be inefficient in terms of image decoding.

According to an embodiment, the decoder 240 may determine third codingunits 1022 a, 1022 b, 1024 a, and 1024 b by splitting, in the verticaldirection, the second coding unit 1020 a or 1020 b having a non-squareshape determined when a first coding unit 900 is split in the horizontaldirection. However, when one of the second coding units (e.g., thesecond coding unit 1020 a at the top) is split in the verticaldirection, the decoder 240 may set a limit so that the other secondcoding unit (e.g., the second coding unit 1020 b at the bottom) is notsplit in the vertical direction like the second coding unit 1020 a atthe top for the above-described reasons.

FIG. 11 illustrates a process by which an image decoding apparatussplits a coding unit having a square shape when split shape informationis unable to indicate that a coding unit is split into four squarecoding units, according to an embodiment.

According to an embodiment, the decoder 240 may determine second codingunits 1110 a, 1110 b, 1120 a, and 1120 b by splitting a first codingunit 1100 based on at least one of block shape information and splitshape information. The split shape information may include informationabout various shapes into which a coding unit may be split, but suchinformation about various shapes may not include information forsplitting a coding unit into four square coding units. According to suchsplit shape information, the decoder 240 is unable to split the firstcoding unit 1100 having a square shape into four second coding units1130 a through 1130 d having a square shape. The decoder 240 maydetermine the second coding units 1110 a, 1110 b, 1120 a, and 1120 bhaving a non-square shape based on the split shape information.

According to an embodiment, the decoder 240 may independently split eachof the second coding units 1110 a and 1110 b, or 1120 a and 1120 bhaving a non-square shape. The second coding units 1110 a, 1110 b, 1120a, and 1120 b may be split in a predetermined order via a recursivemethod that may be a split method similar to a method of splitting thefirst coding unit 1100 based on at least one of the block shapeinformation and the split shape information.

For example, the decoder 240 may determine third coding units 1112 a and1112 b having a square shape by splitting the second coding unit 1110 aat the left in a horizontal direction, and determine third coding units1114 a and 1114 b having a square shape by splitting the second codingunit 1110 b at the right in the horizontal direction. In addition, thedecoder 240 may determine third coding units 1116 a through 1116 dhaving a square shape by splitting both the second coding unit 1110 a atthe left and the second coding unit 1110 b at the right in thehorizontal direction. In this case, coding units may be determined inthe same manner as when the first coding unit 1100 is split into foursecond coding units 1130 a through 1130 d having a square shape.

As another example, the decoder 240 may determine third coding units1122 a and 1122 b having a square shape by splitting the second codingunit 1120 a at the top in a vertical direction, and determine thirdcoding units 1124 a and 1124 b having a square shape by splitting thesecond coding unit 1120 b at the bottom in the vertical direction. Inaddition, the decoder 240 may determine the third coding units 1122 a,1122 b, 1124 a, and 1124 b having a square shape by splitting both thesecond coding unit 1120 a at the top and the second coding unit 1120 bat the bottom in the vertical direction. In this case, coding units maybe determined in the same manner as when the first coding unit 1100 issplit into the four second coding units 1130 a through 1130 d having asquare shape.

FIG. 12 illustrates that an order of processing a plurality of codingunits may vary according to a process of splitting a coding unit,according to an embodiment.

According to an embodiment, the decoder 240 may split the first codingunit 1200 based on block shape information and split shape information.When the block shape information indicates a square shape and the splitshape information indicates that the first coding unit 1200 is split inat least one of a horizontal direction and a vertical direction, thedecoder 240 may determine the second coding units 1210 a, 1210 b, 1220a, 1220 b, 1230 c, and 1230 d by splitting the first coding unit 1200.Referring to FIG. 12, the second coding units 1210 a 1210 b, 1220 a, and1220 b having a non-square shape and determined by splitting the firstcoding unit 1200 in the horizontal direction or the vertical directionmay be independently split based on block shape information and splitshape information. For example, the decoder 240 may determine the thirdcoding units 1216 a through 1216 d by respectively splitting, in thehorizontal direction, the second coding units 1210 a and 1210 bgenerated as the first coding unit 1200 is split in the verticaldirection, or determine the third coding units 1226 a through 1226 d byrespectively splitting, in the horizontal direction, the second codingunits 1220 a and 1220 b generated as the first coding unit 1200 is splitin the horizontal direction. A process of splitting the second codingunits 1210 a, 1210 b, 1220 a, and 1220 b have been described above withreference to FIG. 10, and thus a detailed explanation thereof will notbe given.

According to an embodiment, the decoder 240 may process coding unitsaccording to a predetermined order. Characteristics about processingcoding units according to a predetermined order have been describedabove, and thus a detailed explanation thereof will not be given.Referring to FIG. 12, the decoder 240 may determine four third codingunits 1216 a through 1216 d or 1226 a through 1226 d having a squareshape by splitting the first coding unit 1200 having a square shape.According to an embodiment, the decoder 240 may determine an order ofprocessing the third coding units 1216 a through 1216 d or 1226 athrough 1226 d based on how the first coding unit 1200 is split.

According to an embodiment, the decoder 240 may determine the thirdcoding units 1216 a through 1216 d by splitting, in the horizontaldirection, the second coding units 1210 a and 1210 b generated as thefirst coding unit 1200 is split in the vertical direction, and mayprocess the third coding units 1216 a through 1216 d according to anorder 1217 of first processing, in the vertical direction, the thirdcoding units 1216 a and 1216 b included in the second coding unit 1210 aat the left, and then processing, in the vertical direction, the thirdcoding units 1216 c and 1216 d included in the second coding unit 1210 bat the right.

According to an embodiment, the decoder 240 may determine the thirdcoding units 1226 a through 1226 d by splitting, in the verticaldirection, the second coding units 1220 a and 1220 b generated as thefirst coding unit 1200 is split in the horizontal direction, and thedecoder 240 may process the third coding units 1226 a through 1226 daccording to an order 1227 of first processing, in the horizontaldirection, the third coding units 1226 a and 1226 b included in thesecond coding unit 1220 a at the top, and then processing, in thehorizontal direction, the third coding units 1226 c and 1226 d includedin the second coding unit 1220 b at the bottom.

Referring to FIG. 12, the third coding units 1216 a through 1216 d or1226 a through 1226 d having a square shape may be determined when thesecond coding units 1210 a and 1210 b, or 1220 a and 1220 b are eachsplit. The second coding units 1210 a and 1210 b determined when thefirst coding unit 1200 is split in the vertical direction and the secondcoding units 1220 a and 1220 b determined when the first coding unit1200 is split in the horizontal direction are split into differentshapes, but according to the third coding units 1216 a through 1216 dand 1226 a through 1226 d determined afterwards, the first coding unit1200 is split into coding units having the same shape. Accordingly, thedecoder 240 may process a plurality of coding units determined to havethe same shape in different orders even when the coding units having thesame shape are consequently determined by recursively splitting codingunits through different processes based on at least one of block shapeinformation and split shape information.

FIG. 13 illustrates a process of determining a depth of a coding unitaccording to a change in a shape and a size of the coding unit when aplurality of coding units are determined as the coding unit isrecursively split, according to an embodiment.

According to an embodiment, the decoder 240 may determine a depth of acoding unit according to a predetermined standard. For example, thepredetermined standard may be a length of a long side of the codingunit. When a length of a long side of a current coding unit is split 2 ntimes shorter than a length of a long side of a coding unit before beingsplit, the decoder 240 may determine that a depth of the current codingunit is increased n times a depth of the coding unit before being split,wherein n>0. Hereinafter, a coding unit having an increased depth isreferred to as a coding unit of a lower depth.

Referring to FIG. 13, the decoder 240 may determine a second coding unit1302 and a third coding unit 1304 of lower depths by splitting a firstcoding unit 1300 having a square shape, based on block shape informationindicating a square shape (e.g., the block shape information mayindicate ‘0:SQUARE’) according to an embodiment. When a size of thefirst coding unit 1300 having a square shape is 2N×2N, the second codingunit 1302 determined by splitting a width and a height of the firstcoding unit 1300 by ½{circumflex over ( )}1 may have a size of N×N. Inaddition, the third coding unit 1304 determined by splitting a width anda height of the second coding unit 1302 by ½ may have a size of N/2×N/2.In this case, a width and a height of the third coding unit 1304corresponds to ½{circumflex over ( )}2 of the first coding unit 1300.When a depth of first coding unit 1300 is D, a depth of the secondcoding unit 1302 having ½{circumflex over ( )}1 of the width and theheight of the first coding unit 1300 may be D+1, and a depth of thethird coding unit 1304 having ½{circumflex over ( )}2 of the width andthe height of the first coding unit 1300 may be D+2.

According to an embodiment, the decoder 240 may determine a secondcoding unit 1312 or 1322 and a third coding unit 1314 or 1324 bysplitting a first coding unit 1310 or 1320 having a non-square shape,based on block shape information indicating a non-square shape (e.g.,the block shape information may indicate ‘1:NS_VER’ indicating anon-square shape in which a height is greater than a width, or‘2:NS_HOR’ indicating a non-square shape in which a width is greaterthan a height) according to an embodiment.

The decoder 240 may determine a second coding unit (e.g., the secondcoding unit 1302, 1312, or 1322) by splitting at least one of a widthand a height of the first coding unit 1310 having a size of N×2N. Inother words, the decoder 240 may determine the second coding unit 1302having a size of N×N or the second coding unit 1322 having a size ofN×N/2 by splitting the first coding unit 1310 in a horizontal direction,or determine the second coding unit 1312 having a size of N/2×N bysplitting the first coding unit 1310 in horizontal and verticaldirections.

According to an embodiment, the decoder 240 may determine a secondcoding unit (e.g., the second coding unit 1302, 1312, or 1322) bysplitting at least one of a width and a height of the first coding unit1320 having a size of 2N×N. In other words, the decoder 240 maydetermine the second coding unit 1302 having a size of N×N or the secondcoding unit 1312 having a size of N/2×N by splitting the first codingunit 1320 in the vertical direction, or determine the second coding unit1322 having a size of N×N/2 by splitting the first coding unit 1320 inthe horizontal and vertical directions.

According to an embodiment, the decoder 240 may determine a third codingunit (e.g., the third coding unit 1304, 1314, or 1324) by splitting atleast one of a width and a height of the second coding unit 1302 havinga size of N×N. In other words, the decoder 240 may determine the thirdcoding unit 1304 having a size of N/2×N/2, the third coding unit 1314having a size of N/2{circumflex over ( )}2×N/2, or the third coding unit1324 having a size of N/2×N/2{circumflex over ( )}2 by splitting thesecond coding unit 1302 in the vertical and horizontal directions.

According to an embodiment, the decoder 240 may determine a third codingunit (e.g., the third coding unit 1304, 1314, or 1324) by splitting atleast one of a width and a height of the second coding unit 1312 havinga size of N/2×N. In other words, the decoder 240 may determine the thirdcoding unit 1304 having a size of N/2×N/2 or the third coding unit 1324having a size of N/2×N/2{circumflex over ( )}2 by splitting the secondcoding unit 1312 in the horizontal direction, or may determine the thirdcoding unit 1314 having a size of N/2{circumflex over ( )}2×N/2 bysplitting the second coding unit 1312 in the vertical and horizontaldirections.

According to an embodiment, the decoder 240 may determine a third codingunit (e.g., the third coding unit 1304, 1314, or 1324) by splitting atleast one of a width and a height of the second coding unit 1314 havinga size of N×N/2. In other words, the decoder 240 may determine the thirdcoding unit 1304 having a size of N/2×N/2 or the third coding unit 1314having a size of N/2{circumflex over ( )}2×N/2 by splitting the secondcoding unit 1312 in the vertical horizontal direction, or may determinethe third coding unit 1324 having a size of N/2×N/2{circumflex over( )}2 by splitting the second coding unit 1312 in the vertical andhorizontal directions.

According to an embodiment, the decoder 240 may split a coding unit(e.g., the first, second, or third coding unit 1300, 1302, or 1304)having a square shape in the horizontal or vertical direction. Forexample, the first coding unit 1310 having a size of N×2N may bedetermined by splitting the first coding unit 1300 having a size of2N×2N in the vertical direction, or the first coding unit 1320 having asize of 2N×N may be determined by splitting the first coding unit 1300in the horizontal direction. According to an embodiment, when a depth isdetermined based on a length of a longest side of a coding unit, a depthof a coding unit determined when the first coding unit 1300, 1302, or1304 having a size of 2N×2N is split in the horizontal or verticaldirection may be the same as a depth of the first coding unit 1300,1302, or 1304.

According to an embodiment, the width and the height of the third codingunit 1314 or 1324 may be ½{circumflex over ( )}2 of those of the firstcoding unit 1310 or 1320. When the depth of the first coding unit 1310or 1320 is D, the depth of the second coding unit 1312 or 1314 that is ½of the width and the height of the first coding unit 1310 or 1320 may beD+1, and the depth of the third coding unit 1314 or 1324 that is½{circumflex over ( )}2 of the width and the height of the first codingunit 1310 or 1320 may be D+2.

FIG. 14 illustrates a PID for distinguishing depths and coding unitsthat may be determined according to shapes and sizes of coding units,according to an embodiment.

According to an embodiment, the decoder 240 may determine second codingunits having various shapes by splitting a first coding unit 1400 havinga square shape. Referring to FIG. 14, the decoder 240 may determinesecond coding units 1402 a, 1402 b, 1404 a, 1404 b, 1406 a, 1406 b, 1406c, and 1406 d by splitting the first coding unit 1400 in at least one ofa vertical direction and a horizontal direction according to split shapeinformation. In other words, the decoder 240 may determine the secondcoding units 1402 a, 1402 b, 1404 a, 1404 b, 1406 a, 1406 b, 1406 c, and1406 d based on the split shape information of the first coding unit1400.

According to an embodiment, a depth of the second coding units 1402 a,1402 b, 1404 a, 1404 b, 1406 a, 1406 b, 1406 c, and 1406 d determinedaccording to the split shape information of the first coding unit 1400having a square shape may be determined based on a length of a longside. For example, since a length of one side of the first coding unit1400 having a square shape is the same as a length of a long side of thesecond coding units 1402 a, 1402 b 1404 a, and 1404 b having anon-square shape, the depths of the first coding unit 1400 and thesecond coding units 1402 a, 1402 b, 1404 a, and 1404 b having anon-square shape may be the same, i.e., D. On the other hand, when thedecoder 240 splits the first coding unit 1400 into the four secondcoding units 1406 a through 1406 d having a square shape, based on thesplit shape information, a length of one side of the second coding units1406 a through 1406 d having a square shape is ½ of the length of oneside of the first coding unit 1400, the depths of the second codingunits 1406 a through 1406 d may be D+1, i.e., a depth lower than thedepth D of the first coding unit 1400.

According to an embodiment, the decoder 240 may split the first codingunit 1410, in which a height is greater than a width, in the horizontaldirection into the plurality of second coding units 1412 a and 1412 b or1414 a through 1414 c, according to split shape information. Accordingto an embodiment, the decoder 240 may split a first coding unit 1420, inwhich a width is greater than a height, in the vertical direction into aplurality of second coding units 1422 a and 1422 b or 1424 a through1424 c, according to split shape information.

According to an embodiment, depths of the second coding units 1412 a and1412 b, 1414 a through 1414 c, 1422 a and 1422 b, or 1424 a through 1424c determined according to the split shape information of the firstcoding unit 1410 or 1420 having a non-square shape may be determinedbased on a length of a long side. For example, since a length of oneside of the second coding units 1412 a and 1412 b having a square shapeis ½ of a length of one side of the first coding unit 1410 having anon-square shape, in which the height is greater than the width, thedepths of the second coding units 1402 a, 1402 b, 1404 a, and 1404 bhaving a square shape are D+1, i.e., depths lower than the depth D ofthe first coding unit 1410 having a non-square shape.

In addition, the decoder 240 may split the first coding unit 1410 havinga non-square shape into an odd number of second coding units 1414 athrough 1414 c based on split shape information. The odd number ofsecond coding units 1414 a through 1414 c may include the second codingunits 1414 a and 1414 c having a non-square shape, and the second codingunit 1414 b having a square shape. In this case, since a length of along side of each of the second coding units 1414 a and 1414 c having anon-square shape and a length of one side of the second coding unit 1414b having a square shape are ½ of a length of one side of the firstcoding unit 1410, depths of the second coding units 1414 a through 1414b may be D+1, i.e., a depth lower than the depth D of the first codingunit 1410. The decoder 240 may determine depths of coding units relatedto the first coding unit 1420 having a non-square shape in which a widthis greater than a height, in the same manner as the determining ofdepths of coding units related to the first coding unit 1410.

According to an embodiment, with respect to determining PIDs fordistinguishing coding units, when an odd number of coding units do nothave the same size, the decoder 240 may determine PIDs based on a sizeratio of the coding units. Referring to FIG. 14, the second coding unit1414 b located at the center from among the odd number of second codingunits 1414 a through 1414 c may have the same width as the second codingunits 1414 a and 1414 c, but may have a height twice greater than thoseof the second coding units 1414 a and 1414 c. In this case, the secondcoding unit 1414 b located at the center may include two of the secondcoding units 1414 a and 1414 c. Accordingly, when the PID of the secondcoding unit 1414 b located at the center is 1 according to a scan order,the PID of the second coding unit 1414 c in a next order may be 3, thePID having increased by 2. In other words, values of the PID may bediscontinuous. According to an embodiment, the decoder 240 may determinewhether an odd number of coding units have the same sizes based ondiscontinuity of PIDs for distinguishing the coding units.

(Determination of Tri-Split Using PID)

According to an embodiment, an image decoding apparatus may determinewhether a plurality of coding units determined when a current codingunit is split have predetermined split shapes based on values of PIDs.Referring to FIG. 14, the image decoding apparatus may determine theeven number of second coding units 1412 a and 1412 b or the odd numberof second coding units 1414 a through 1414 c by splitting the firstcoding unit 1410 having a rectangular shape in which the height isgreater than the width. The image decoding apparatus may use a PIDindicating each coding unit so as to distinguish a plurality of codingunits. According to an embodiment, the PID may be obtained from a sampleat a predetermined location (e.g., an upper left sample) of each codingunit.

According to an embodiment, the image decoding apparatus may determine acoding unit at a predetermined location from among coding unitsdetermined by using PIDs for distinguishing coding units. According toan embodiment, when split shape information of the first coding unit1410 having a rectangular shape in which a height is greater than awidth indicates that the first coding unit 1410 is split into threecoding units, the image decoding apparatus may split the first codingunit 1410 into the three second coding units 1414 a through 1414 c. Theimage decoding apparatus may assign a PID to each of the three secondcoding units 1414 a through 1414 c. The image decoding apparatus maycompare PIDs of an odd number of coding units so as to determine acenter coding unit from among the coding units. The image decodingapparatus may determine, as a coding unit at a center location fromamong coding units determined when the first coding unit 1410 is split,the second coding unit 1414 b having a PID corresponding to a centervalue from among PIDs, based on PIDs of the coding units. According toan embodiment, while determining PIDs for distinguishing coding units,when the coding units do not have the same size, the image decodingapparatus may determine PIDs based on a size ratio of the coding units.Referring to FIG. 14, the second coding unit 1414 b generated when thefirst coding unit 1410 is split may have the same width as the secondcoding units 1414 a and 1414 c, but may have a height twice greater thanthose of the second coding units 1414 a and 1414 c. In this case, whenthe PID of the second coding unit 1414 b located at the center is 1, thePID of the second coding unit 1414 c in a next order may be 3, the PIDhaving increased by 2. As such, when an increasing range of PIDs differswhile uniformly increasing, the image decoding apparatus may determinethat a current coding unit is split into a plurality of coding unitsincluding a coding unit having a different size from other coding units.According to an embodiment, when split shape information indicatessplitting into an odd number of coding units, the image decodingapparatus may split a current coding unit into a plurality of codingunits, in which a coding unit at a predetermined location (e.g., acenter coding unit) has a size different from other coding units. Inthis case, the image decoding apparatus may determine the center codingunit having the different size by using PIDs of the coding units.However, a PID, and a size or location of a coding unit at apredetermined location described above are specified to describe anembodiment, and thus should not be limitedly interpreted, and variousPIDs, and various locations and sizes of coding units may be used.

According to an embodiment, the decoder 240 may use a predetermined dataunit from which recursive splitting of a coding unit starts.

FIG. 15 illustrates that a plurality of coding units are determinedaccording to a plurality of predetermined data units included in apicture, according to an embodiment.

According to an embodiment, a predetermined data unit may be defined asa data unit from which a coding unit starts to be recursively split byusing at least one of block shape information and split shapeinformation. In other words, the predetermined data unit may correspondto a coding unit of an uppermost depth used while determining aplurality of coding units by splitting a current picture. Hereinafter,the predetermined data unit is referred to as a reference data unit forconvenience of description.

According to an embodiment, the reference data unit may indicate apredetermined size and shape. According to an embodiment, the referencedata unit may include M×N samples. Here, M and N may be the same, andmay be an integer represented as a multiple of 2. In other words, thereference data unit may indicate a square shape or a non-square shape,and may later be split into an integer number of coding units.

According to an embodiment, the decoder 240 of the image decodingapparatus may split a current picture into a plurality of reference dataunits. According to an embodiment, the decoder 240 may split theplurality of reference data units obtained by splitting the currentpicture by using split shape information about each of the referencedata units. A process of splitting the reference data units maycorrespond to a split process using a quad-tree structure.

According to an embodiment, the decoder 240 may pre-determine a smallestsize available for the reference data unit included in the currentpicture. Accordingly, the decoder 240 may determine the reference dataunit having various sizes that are equal to or larger than the smallestsize, and may determine at least one coding unit based on the determinedreference data unit by using block shape information and split shapeinformation.

Referring to FIG. 15, the image decoding apparatus may use the referencecoding unit 1500 having a square shape, or may use a reference codingunit 1502 having a non-square shape. According to an embodiment, a shapeand size of a reference coding unit may be determined according tovarious data units (e.g., a sequence, a picture, a slice, a slicesegment, and a largest coding unit) that may include at least onereference coding unit.

According to an embodiment, a bitstream obtainer of the image decodingapparatus may obtain, from a bitstream, at least one of informationabout a shape of a reference coding unit and information about a size ofthe reference coding unit, according to the various data units. Aprocess of determining at least one coding unit included in thereference coding unit 1500 having a square shape has been describedabove, and a process of determining at least one coding unit included inthe reference coding unit 1500 having a non-square shape has beendescribed above, and thus a detailed explanation thereof will not begiven.

According to an embodiment, in order to determine a size and shape of areference coding unit according to some data units pre-determined basedon a predetermined condition, the decoder 240 may use a PID fordistinguishing the size and the shape of the reference coding unit. Inother words, the bitstream obtainer may obtain, from a bitstream, onlythe PID for distinguishing the size and the shape of the referencecoding unit as a data unit satisfying a predetermined condition (e.g., adata unit having a size equal to or smaller than a slice) from amongvarious data units (e.g., a sequence, a picture, a slice, a slicesegment, and a largest coding unit), according to slices, slicesegments, and largest coding units. The decoder 240 may determine thesize and shape of the reference data unit according to data units thatsatisfy the predetermined condition by using the PID. When informationabout the shape of the reference coding unit and information about thesize of the reference coding unit are obtained from the bitstream andused according to data units having relatively small sizes, usageefficiency of the bitstream may not be sufficient, and thus instead ofdirectly obtaining the information about the shape of the referencecoding unit and the information about the size of the reference codingunit, only the PID may be obtained and used. In this case, at least oneof the size and the shape of the reference coding unit corresponding tothe PID indicating the size and shape of the reference coding unit maybe pre-determined. In other words, the decoder 240 may select at leastone of the pre-determined size and shape of the reference coding unitaccording to the PID so as to determine at least one of the size andshape of the reference coding unit included in a data unit that is acriterion for obtaining the PID.

According to an embodiment, the decoder 240 may use at least onereference coding unit included in one largest coding unit. In otherwords, a largest coding unit splitting an image may include at least onereference coding unit, and a coding unit may be determined when eachreference coding unit is recursively split. According to an embodiment,at least one of a width and height of the largest coding unit may be aninteger times at least one of a width and height of the reference codingunit. According to an embodiment, a size of the reference coding unitmay be equal to a size of the largest coding unit that is split n timesaccording to a quad-tree structure. In other words, the decoder 240 maydetermine the reference coding unit by splitting the largest coding unitn times according to the quad-tree structure, and may split thereference coding unit based on at least one of block shape informationand split shape information according to various embodiments.

FIG. 16 illustrates a processing block that becomes a criterion fordetermining a determining order of reference coding units included inthe picture 1600, according to an embodiment.

According to an embodiment, the decoder 240 may determine at least oneprocessing block splitting a picture. A processing block is a data unitincluding at least one reference coding unit splitting an image, and theat least one reference coding unit included in the processing block maybe determined in a predetermined order. In other words, a determiningorder of the at least one reference coding unit determined in eachprocessing block may correspond to one of various orders for determininga reference coding unit, and may vary according to processing blocks. Adetermining order of reference coding units determined per processingblock may be one of various orders, such as a raster scan order, aZ-scan order, an N-scan order, an up-right diagonal scan order, ahorizontal scan order, and a vertical scan order, but should not belimitedly interpreted with respect to the scan orders.

According to an embodiment, the decoder 240 may obtain information abouta size of a processing block and may determine a size of at least oneprocessing block included in an image. The decoder 240 may obtain, froma bitstream, the information about a size of a processing block and maydetermine the size of the at least one processing block included in theimage. The size of the processing block may be a predetermined size of adata unit indicated by the information about a size of a processingblock.

According to an embodiment, a bitstream obtainer of an image decodingapparatus may obtain, from the bitstream, the information about a sizeof a processing block according to predetermined data units. Forexample, the information about a size of a processing block may beobtained from the bitstream in data units such as images, sequences,pictures, slices, and slice segments. In other words, the bitstreamobtainer may obtain, from the bitstream, the information about a size ofa processing block according to such several data units, and the decoder240 may determine the size of at least one processing block splittingthe picture by using the obtained information about a size of aprocessing block, wherein the size of the processing block may be aninteger times a size of a reference coding unit.

According to an embodiment, the decoder 240 may determine sizes of theprocessing blocks 1602 and 1612 included in the picture 1600. Forexample, the decoder 240 may determine a size of a processing blockbased on information about a size of a processing block obtained from abitstream. Referring to FIG. 16, the decoder 240 may determinehorizontal sizes of the processing blocks 1602 and 1612 to be four timesa horizontal size of a reference coding unit, and vertical sizes thereofto be four times a vertical size of the reference coding unit, accordingto an embodiment. The decoder 240 may determine a determining order ofat least one reference coding unit in at least one processing block.

According to an embodiment, the decoder 240 may determine each of theprocessing blocks 1602 and 1612 included in the picture 1600 based on asize of a processing block, and a reference coding unit determiner maydetermine a determining order of at least one reference coding unitincluded in each of the processing blocks 1602 and 1612. According to anembodiment, determining of a reference coding unit may includedetermining a size of the reference coding unit.

According to an embodiment, the decoder 240 may obtain, from abitstream, information about a determining order of at least onereference coding unit included in at least one processing block, and maydetermine the determining order of the at least one reference codingunit based on the obtained information. The information about adetermining order may be defined as an order or direction of determiningreference coding units in a processing block. In other words, an orderof determining reference coding units may be independently determinedper processing block.

According to an embodiment, the image decoding apparatus may obtain,from a bitstream, information about a determining order of a referencecoding unit according to predetermined data units. For example, thebitstream obtainer may obtain, from the bitstream, the information abouta determining order of a reference coding unit according to data units,such as images, sequences, pictures, slices, slice segments, andprocessing blocks. Since the information about a determining order of areference coding unit indicates a determining order of a referencecoding unit in a processing block, the information about a determiningorder may be obtained per predetermined data unit including an integernumber of processing blocks.

According to an embodiment, the image decoding apparatus may determineat least one reference coding unit based on the determined order.

According to an embodiment, the bitstream obtainer may obtain, from thebitstream, information about a determining order of a reference codingunit, as information related to the processing blocks 1602 and 1612, andthe decoder 240 may determine an order of determining at least onereference coding unit included in the processing blocks 1602 and 1612and may determine at least one reference coding unit included in thepicture 1600 according to a determining order of a coding unit.Referring to FIG. 16, the decoder 240 may determine determining orders1604 and 1614 of at least one reference coding unit respectively relatedto the processing blocks 1602 and 1612. For example, when informationabout a determining order of a reference coding unit is obtained perprocessing block, determining orders of a reference coding unit relatedto the processing blocks 1602 and 1612 may be different from each other.When the determining order 1604 related to the processing block 1602 isa raster scan order, reference coding units included in the processingblock 1602 may be determined according to the raster scan order. On theother hand, when the determining order 1614 related to the processingblock 1612 is a reverse order of a raster scan order, reference codingunits included in the processing block 1612 may be determined in thereverse order of the raster scan order.

The decoder 240 may decode determined at least one reference coding unitaccording to an embodiment. The decoder 240 may decode an image based onreference coding units determined through the above embodiments.Examples of a method of decoding a reference coding unit may includevarious methods of decoding an image.

According to an embodiment, the image decoding apparatus may obtain,from a bitstream, and use block shape information indicating a shape ofa current coding unit or split shape information indicating a method ofsplitting the current coding unit. The block shape information or thesplit shape information may be included in a bitstream related tovarious data units. For example, the image decoding apparatus may usethe block shape information or split shape information, which isincluded in a sequence parameter set, a picture parameter set, a videoparameter set, a slice header, and a slice segment header. In addition,the image decoding apparatus may obtain, from a bitstream, and usesyntax corresponding to the block shape information or the split shapeinformation, according to largest coding units, reference coding units,and processing blocks.

According to an embodiment, the decoder 240 may differently determine atype of split shapes into which a coding unit may be split according topredetermined data units. The decoder 240 of the image decodingapparatus may differently determine a combination of shapes into which acoding unit may be split according to predetermined data units (e.g.,sequences, pictures, and slices) according to an embodiment.

FIG. 17 illustrates coding units that may be determined for each picturewhen combinations of shapes into which a coding unit may be split aredifferent, according to an embodiment.

Referring to FIG. 17, the decoder 240 may differently determine acombination of split shapes into which a coding unit may be split foreach picture. For example, the decoder 240 may decode an image by usingthe picture 1700 that may be split into four coding units, the picture1710 that may be split into two or four coding units, and the picture1720 that may be split into two, three, or four coding units from amongone or more pictures included in the image. The decoder 240 may use onlysplit shape information indicating that the picture 1700 is split intofour square coding units in order to split the picture 1700 into aplurality of coding units. The decoder 240 may use only split shapeinformation indicating that the picture 1710 is split into two or fourcoding units in order to split the picture 1710. The decoder 240 may useonly split shape information indicating that the picture 1720 is splitinto two, three, or four coding units in order to split the picture1720. Since the combination of split shapes is merely an embodiment fordescribing an operation of the image decoding apparatus, the combinationof the split shapes should not be interpreted as being limited to theembodiment and various combinations of split shapes may be usedaccording to predetermined data units.

According to an embodiment, a bitstream obtainer of the image decodingapparatus may obtain a bitstream including an index indicating acombination of split shape information according to predetermined dataunits (e.g., sequences, pictures, and slices). For example, thebitstream obtainer may obtain an index indicating a combination of splitshape information in a sequence parameter set, a picture parameter set,or a slice header. The decoder 240 of the image decoding apparatus maydetermine a combination of split shapes into which a coding unit may besplit according to predetermined data units by using the obtained index,and thus a different combination of split shapes may be used accordingto predetermined data units.

FIG. 18 illustrates various shapes of a coding unit that may bedetermined based on split shape information that may be represented as abinary code, according to an embodiment.

According to an embodiment, an image decoding apparatus may split acoding unit into various shapes by using block shape information andsplit shape information obtained by a bitstream obtainer. Shapes intowhich a coding unit may be split may correspond to various shapesincluding shapes described with reference to the above embodiments.

Referring to FIG. 18, the decoder 240 may split a coding unit having asquare shape in at least one of a horizontal direction and a verticaldirection and may split a coding unit having a non-square shape in thehorizontal direction or the vertical direction based on split shapeinformation.

According to an embodiment, when the decoder 240 may split a coding unithaving a square shape in the horizontal direction and the verticaldirection into four square coding units, the number of split shapes thatmay be indicated by split shape information about the coding unit havinga square shape may be 4. According to an embodiment, split shapeinformation may be represented as a two-digit binary code, and a binarycode may be assigned to each split shape. For example, when a codingunit is not split, the split shape information may be represented as(00)b; when a coding unit is split in the horizontal direction and thevertical direction, the split shape information may be represented as(01)b; when a coding unit is split in the horizontal direction, thesplit shape information may be represented as (10)b; and when a codingunit is split in the vertical direction, the split shape information maybe represented as (11)b.

According to an embodiment, when the decoder 240 splits a coding unithaving a non-square shape in the horizontal direction or the verticaldirection, types of split shapes that may be indicated by split shapeinformation may be determined according to the number of coding unitsinto which the coding unit having a non-square shape is split. Referringto FIG. 18, the decoder 240 may split a coding unit having a non-squareshape into up to three coding units according to an embodiment. Thedecoder 240 may split a coding unit into two coding units, and in thiscase, the split shape information may be represented as (10)b. Thedecoder 240 may split a coding unit into three coding units, and in thiscase, the split shape information may be represented as (11)b. Thedecoder 240 may determine that a coding unit is not split, and in thiscase, the split shape information may be represented as (0)b. That is,the decoder 240 may use VLC, instead of FLC, in order to use a binarycode indicating the split shape information.

According to an embodiment, referring to FIG. 18, a binary code of splitshape information indicating that a coding unit is not split may berepresented as (0)b. If a binary code of split shape informationindicating that a coding unit is not split is set to (00)b, althoughthere is no split shape information set to (01)b, all two-bit binarycodes of split shape information have to be used. However, as shown inFIG. 18, when three split shapes are used for a coding unit having anon-square shape, the decoder 240 may determine that a coding unit isnot split although a one-bit binary code (0)b is used as split shapeinformation, thereby efficiently using a bitstream. However, shapes intowhich a coding unit having a non-square shape is split which may beindicated by split shape information should not be interpreted as beinglimited to three shapes of FIG. 18, and should be interpreted as beingvarious shapes including the above embodiments.

FIG. 19 illustrates other shapes of a coding unit that may be determinedbased on split shape information that may be represented as a binarycode, according to an embodiment.

Referring to FIG. 19, the decoder 240 may split a coding unit having asquare shape in a horizontal direction or a vertical direction and maysplit a coding unit having a non-square shape in the horizontaldirection or the vertical direction based on split shape information.That is, split shape information may indicate that a coding unit havinga square shape is split only in one direction. In this case, a binarycode of split shape information indicating that a coding unit having asquare shape is not split may be represented as (0)b. If a binary codeof split shape information indicating that a coding unit is not split isset to (00)b, although there is no split shape information set to (01)b,all two-bit binary codes of split shape information have to be used.However, as shown in FIG. 19, when three split shapes are used for acoding unit having a square shape, the decoder 240 may determine that acoding unit is not split although a one-bit binary code (0)b is used assplit shape information, thereby efficiently using a bitstream. Shapeinto which a coding unit having a square shape is split which may beindicated by split shape information should not be interpreted as beinglimited to three shapes of FIG. 19, and should be interpreted as beingvarious shapes including the above embodiments.

According to an embodiment, block shape information or split shapeinformation may be represented by using a binary code, and suchinformation may be directly generated as a bitsream. Also, block shapeinformation or split shape information that may be represented as abinary code may be used as a binary code input during context adaptivebinary arithmetic coding (CABAC), without being directly generated as abitstream.

According to an embodiment, a process by which an image decodingapparatus obtains syntax about block shape information or split shapeinformation through CABAC will be described. A bitstream obtainer mayobtain a bitstream including a binary code for the syntax. The decoder240 may detect a syntax element indicating the block shape informationor the split shape information by de-binarizing a bin string included inthe obtained bitstream. According to an embodiment, the decoder 240 mayobtain a set of binary bin strings corresponding to the syntax elementto be decoded and may decode each bin by using probability information,and the decoder 240 may repeatedly perform this process until a binstring including such decoded bins is the same as one of pre-obtainedbin strings. The decoder 240 may determine the syntax element byde-binarizing the bin string.

According to an embodiment, the decoder 240 may determine syntax about abin string by performing a decoding process of adaptive binaryarithmetic coding, and may update a probability model for bins obtainedby the bitstream obtainer. Referring to FIG. 18, the bitstream obtainerof the image decoding apparatus may obtain a bitstream indicating abinary code indicating split shape information according to anembodiment. The decoder 240 may determine syntax about the split shapeinformation by using the obtained binary code having a size of 1 bit or2 bits. The decoder 240 may update a probability of each bit from amongthe 2 bits of the binary code in order to determine the syntax about thesplit shape information. That is, the decoder 240 may update aprobability that may have a value of 0 or 1 when decoding a next binaccording to whether a value of a first bin in the 2 bits of the binarycode is 0 or 1.

According to an embodiment, while determining the syntax, the decoder240 may update a probability of the bins used in a process of decodingthe bins of the bin string for the syntax, and the decoder 240 maydetermine that a specific bit in the bin string has the same probabilitywithout updating the probability.

Referring to FIG. 18, while determining syntax by using a bin stringindicating split shape information about a coding unit having anon-square shape, the decoder 240 may determine the syntax about thesplit shape information by using one bin having a value of 0 when thecoding unit having a non-square shape is not split. That is, when blockshape information indicates that a current coding unit has a non-squareshape, a first bin of a bin string for the split shape information maybe 0 when the coding unit having a non-square shape is not split and maybe 1 when the coding unit having a non-square shape is split into two orthree coding units. Accordingly, a probability that a first bin of a binstring of split shape information about a coding unit having anon-square shape is 0 may be ⅓ and a probability that the first bin ofthe bin string of the split shape information about the coding unithaving a non-square shape is 1 may be ⅔. As described above, split shapeinformation indicating that a coding unit having a non-square shape isnot split may represent only a bin string of 1 bit having a value of 0,the decoder 240 may determine syntax about the split shape informationby determining whether a second bin is 0 or 1 only when the first bin ofthe split shape information is 1. According to an embodiment, when thefirst bin for the split shape information is 1, the decoder 240 maydecode a bin by determining that probabilities that the second bin is 0or 1 are the same.

According to an embodiment, an image decoding apparatus may use variousprobabilities for each bin while determining a bin of a bin string forsplit shape information. According to an embodiment, the decoder 240 maydifferently determine probabilities of bins for split shape informationbased on a direction of a non-square block. According to an embodiment,the decoder 240 may differently determine probabilities of bins forsplit shape information based on an area or a length of a long side of acurrent coding unit. According to an embodiment, the decoder 240 maydifferently determine probabilities of bins for split shape informationbased on at least one from among a shape and a length of a long side ofa current coding unit.

According to an embodiment, the decoder 240 may determine thatprobabilities of bins for split shape information are the same withrespect to coding units having a predetermined size or more. Forexample, the decoder 240 may determine that probabilities of bins forsplit shape information are the same with respect to coding units havinga size equal to or greater than 64 samples based on a length of a longside of each coding unit.

According to an embodiment, the decoder 240 may determine an initialprobability of bins constituting a bin string of split shape informationbased on a slice type (e.g., an I-slice, a P-slice, or a B-slice).

FIG. 20 is a block diagram of an image encoding and decoding system 2000for performing loop filtering.

An encoding end 2010 of the image encoding and decoding system 2000transmits an encoded bitstream of an image, and a decoding end 2050receives and decodes the bitstream and outputs a reconstruction image.The encoding end 2010 may have a configuration similar to that of animage encoding apparatus 200 which will be described below, and thedecoding end 2050 may have a configuration similar to that of an imagedecoding apparatus.

In the encoding end 2010, a prediction encoder 2015 outputs a referenceimage through inter prediction and intra prediction, and a transformerand quantizer 2020 quantizes residual data between the reference imageand a current input image into a quantized transform coefficient andoutputs the quantized transform coefficient. An entropy encoder 2025encodes and transforms the quantized transform coefficient into abitstream and outputs the bitstream. The quantized transform coefficientis reconstructed as data in a spatial domain by a de-quantizer andinverse converter 2030, and the reconstructed data in the spatial domainis output as a reconstruction image through a deblocking filter 2035 anda loop filter 2040. The reconstruction image may be used as a referenceimage of a next input image through the prediction encoder 2015.

Encoded image data from among the bitstream received by the decoding end2050 is reconstructed as residual data in a spatial domain through anentropy decoder 2055 and a de-quantizer and inverse converter 2060.Image data in a spatial domain is formed as the residual data and areference image output from a prediction decoder 2075 are combined, anda deblocking filter 2065 and a loop filter 2070 may filter the imagedata in the spatial domain and may output a reconstruction image for acurrent original image. The reconstruction image may be used as areference image for a next original image by the prediction decoder2075.

The loop filter 2040 of the encoding end 2010 performs loop filtering byusing filter information input according to a user input or a systemsetting. The filter information used by the loop filter 2040 is outputfrom the entropy encoder 2010, and is transmitted along with the encodedimage data to the decoding end 2050. The loop filter 2070 of thedecoding end 2050 may perform loop filtering based on the filterinformation input from the decoding end 2050.

FIG. 21 illustrates an example of filtering units included in a largestcoding unit and filtering performance information of a filtering unit,according to an embodiment.

When filtering units of the loop filter 2040 of the encoding end 2010and the loop filter 2070 of the decoding end 2050 include data unitssimilar to coding units according to an embodiment described withreference to FIGS. 3 through 5, filter information may include blockshape information and split shape information of a data unit forindicating a filtering unit, and loop filtering performance informationindicating whether loop filtering is performed on the filtering unit.

Filtering units included in a largest coding unit 2100 according to anembodiment may have the same block shape and split shape as coding unitsincluded in the largest coding unit 2100. Also, the filtering unitsincluded in the largest coding unit 2100 according to an embodiment maybe split based on sizes of the coding units included in the maximumcoding units 2100. Referring to FIG. 21, for example, the filteringunits may include a filtering unit 2140 having a square shape and adepth of D, filtering units 2132 and 2134 having a non-square shape anda depth of D, filtering units 2112, 2114, 2116, 2152, 2154, and 2164having a square shape and a depth of D+1, filtering units 2162 and 2166having a non-square shape and a depth of D+1, and filtering units 2122,2124, 2126, and 2128 having a square shape and a depth of D+2.

The block shape information, the split shape information (depth), andthe loop filtering performance information of the filtering unitsincluded in the largest coding unit 2100 may be encoded as shown inTable 1.

TABLE 1 Block ratio First block Whether to change and information shapeshape after change 0000 2Nx2N 2Nx2N 0001 NxN NxN 0010 2NxN 2NxnU 00112NxN 0100 Nx2N nLx2N 0101 Nx2N 0110 nLx2N Nx2N 0111 nLx2N 1000 nRx2NNx2N 1001 nRx2N 1010 eNxnU 2NxN 1011 2NxnU 1100 2NxnD 2NxN 1101 2NxnD

A process of determining a plurality of coding units by recursivelysplitting a coding unit according to block shape information and blocksplit information according to an embodiment is the same as thatdescribed with reference to FIG. 13. Loop filtering performanceinformation of filtering units according to an embodiment indicates thatloop filtering is performed on the filtering units when a flag value is1, and indicates that loop filtering is not performed on the filteringunits when a flag value is 0. Referring to Table 1, information of dataunits for determining filtering units to be filtered by the loop filters2040 and 2070 may all be encoded and transmitted as filter information.

Since coding units configured according to an embodiment are codingunits configured to minimize an error with an original image, it isexpected to have a high spatial correlation in the coding units.Accordingly, since a filtering unit is determined based on a coding unitaccording to an embodiment, an operation of determining a filteringunit, separate from determining of a coding unit, may be omitted. Also,accordingly, since a filtering unit is determined based on a coding unitaccording to an embodiment and thus information for determining a splitshape of the filtering unit may be omitted, a transfer bit rate offilter information may be saved.

Although it is described in the above embodiments that a filtering unitis determined based on a coding unit according to an embodiment, afiltering unit may be split based on a coding unit until an arbitrarydepth, and thus a shape of the filtering unit may be determined up toonly the arbitrary depth.

The determining of a filtering unit described in the above embodimentsmay be applied not only to loop filtering but also to variousembodiments such as deblocking filtering and adaptive loop filtering.

According to an embodiment, an image decoding apparatus may split acurrent coding unit by using at least one of block shape information andsplit shape information, and the block shape information may bepre-determined to indicate using only a square shape and the split shapeinformation may be pre-determined to indicate that the current codingunit is not split or split into four square coding units. That is,coding units of the current coding unit may always have a square shapeaccording to the block shape information and the current coding unit maynot be split or split into four square coding units based on the splitshape information. The image decoding apparatus may obtain, by using abitstream obtainer, a bitstream generated by using a predeterminedencoding method that is pre-determined to only use such block shapes andsplit shapes, and the decoder 240 may use only the pre-determined blockshapes and split shapes. In this case, since the image decodingapparatus may solve a compatibility problem with the predeterminedencoding method by using a predetermined decoding method similar to thepredetermined encoding method. According to an embodiment, when theimage decoding apparatus uses the predetermined decoding method usingonly the pre-determined block shapes and split shapes from among variousshapes that may be indicated by the block shape information and thesplit shape information, the block shape information only indicates asquare shape, and thus the image decoding apparatus may not perform aprocess of obtaining the block shape information from the bitstream.Syntax indicating whether to use the predetermined decoding method maybe used, and such syntax may be obtained from the bitstream according todata units having various shapes that may include a plurality of codingunits such as sequences, pictures, slice units, and largest codingunits. That is, the bitstream obtainer may determine whether syntaxindicating the block shape information is to be obtained from thebitstream based on syntax indicating whether the predetermined decodingmethod is used.

FIG. 23 illustrates an index according to a Z-scan order of a codingunit according to an embodiment.

An image decoding apparatus according to an embodiment may scan lowerdata units included in an upper data unit according to a Z-scan order.Also, the image decoding apparatus according to an embodiment maysequentially access data according to a Z-scan index in a coding unitincluded in a processing block or a largest coding unit.

The image decoding apparatus according to an embodiment may split areference coding unit into at least one coding unit as described above.In this case, coding units having a square shape and coding units havinga non-square shape may co-exist in the reference coding unit. The imagedecoding apparatus according to an embodiment may access data accordingto a Z-scan index included in each coding unit in the reference codingunit. In this case, a method of applying a Z-scan index may varyaccording to whether a coding unit having a non-square shape exists inthe reference coding unit.

According to an embodiment, when a coding unit having a non-square shapedoes not exist in the reference coding unit, coding units of a lowerdepth in the reference coding unit may have continuous Z-scan indices.For example, according to an embodiment, a coding unit of an upper depthmay include four coding units of a lower depth. Boundaries of the fourcoding units of the lower depth may be continuous, and the coding unitsof the lower depth may be scanned in a Z-scan order according to indicesindicating the Z-scan order. The indices indicating the Z-scan orderaccording to an embodiment may be set to numbers that increase accordingto the Z-scan order for the coding units. In this case, deeper codingunits of the same depth may be scanned according to the Z-scan order.

According to an embodiment, when at least one coding unit having anon-square shape exists in the reference coding unit, the image decodingunit may split each of the coding units in the reference coding unitinto sub-blocks, and may scan the split sub-blocks according to theZ-scan order. For example, when a coding unit having a non-square shapein a vertical shape or a horizontal shape exists in the reference codingunit, Z-scan may be performed by using split sub-blocks. Also, forexample, when the reference coding unit is split into an odd number ofcoding units, Z-scan may be performed by using sub-blocks. A sub-blockis a coding unit that is no longer split or a coding unit obtained bysplitting an arbitrary coding unit, and may have a square shape. Forexample, four sub-blocks having a square shape may be split from acoding unit having a square shape. Also, for example, two sub-blockshaving a square shape may be split form a coding unit having anon-square shape.

Referring to FIG. 23, for example, the image decoding apparatusaccording to an embodiment may scan coding units 2302, 2304, 2306, 2308,and 2310 of a lower depth in a coding unit 2300 according to a Z-scanorder. The coding unit 2300 and the coding units 2302, 2304, 2306, 2308,and 2310 are respectively an upper coding unit and lower coding units.The coding unit 2300 includes the coding units 2306 and 2310 having anon-square shape in a horizontal direction. The coding units 2306 and2310 having a non-square shape have discontinuous boundaries with thecoding units 2302 and 2304 having a square shape. Also, the coding unit2308 has a square shape, and is a coding unit at the center when acoding unit having a non-square shape is split into an odd number ofcoding units. Like the coding units 2306 and 2310 having a non-squareshape, the coding unit 2308 has discontinuous boundaries with the codingunits 2302 and 2304 that are adjacent to each other and have a squareshape. When the coding unit 2300 includes the coding units 2306 and 2310having a non-square shape or the coding unit 2308 located at the centerwhen a coding unit having a non-square shape is split into an odd numberof coding units, since adjacent boundaries between coding units arediscontinuous, continuous Z-scan indices may not be set. Accordingly,the image decoding apparatus may continuously set Z-scan indices bysplitting coding units into sub-blocks. Also, the image decodingapparatus may perform continuous Z-scan on the coding units 2306 and2310 having a non-square shape or the coding unit 2308 located at thecenter of an odd number of coding units having a non-square shape.

A coding unit 2320 of FIG. 23 is obtained by splitting the coding units2302, 2304, 2306, 2308, and 2310 in the coding unit 2300 intosub-blocks. Since a Z-scan index may be set for each of the sub-blocks,and adjacent boundaries between the sub-blocks are continuous, thesub-blocks may be scanned according to a Z-scan order. For example, in adecoding apparatus according to an embodiment, the coding unit 2308 maybe split into sub-blocks 2322, 2324, 2326 and 2328. In this case, thesub-blocks 2322 and 2324 may be scanned after data processing isperformed on a sub-block 2330, and the sub-blocks 2326 and 2328 may bescanned after data processing is performed on a sub-block 2332. Also,the sub-blocks may be scanned according to the Z-scan order.

In the above embodiments, data units are scanned according to a Z-scanorder for data storage, data loading, and data accessing.

Also, in the above embodiments, although data units may be scannedaccording to a Z-scan order, a scan order of data units may vary, forexample, a raster scan order, an N-scan order, an up-right diagonal scanorder, a horizontal scan order, and a vertical scan order, and shouldnot be limited to the Z-scan order.

Also, in the above embodiments, although coding units in a referencecoding unit are scanned, the present disclosure is not limited theretoand a target to be scanned may be an arbitrary block in a processingblock or a largest coding unit.

Also, in the above embodiments, although a block is split intosub-blocks and scanning is performed according to a Z-scan order onlywhen at least one block having a non-square shape exists, a block may besplit into sub-blocks and scanning may be performed according to aZ-scan order even when a block having a non-square shape does not existfor a simplified embodiment.

The image decoding apparatus according to an embodiment may generateprediction data by performing inter prediction or intra prediction on acoding unit, may generate residual data by performing inversetransformation on a transform unit included in a current coding unit,and may reconstruct the current coding unit by using the generatedprediction data and the residual data.

A prediction mode of a coding unit according to an embodiment may be atleast one of an intra mode, an inter mode, and a skip mode. According toan embodiment, a prediction mode may be independently selected accordingto coding units.

When a coding unit having a 2N×2N shape is split into two coding unitshaving a 2N×N shape or a N×2N shape according to an embodiment, intermode prediction and intra mode prediction may be separately performed oneach coding unit. Also, a skip mode may be applied to the coding unitshaving the 2N×N or N×2N shape according to an embodiment.

The image decoding apparatus according to an embodiment may allowperforming bi-prediction in a skip mode of a coding unit having a 8×4 or4×8 shape. Since only skip mode information about a coding unit isreceived in a skip mode, the use of residual data for the coding unit isomitted. Accordingly, in this case, an overhead of de-quantization andinverse transformation may be reduced. Instead, the image decodingapparatus according to an embodiment may allow performing bi-predictionon a coding unit to which a skip mode is applied, so as to improvedecoding efficiency. Also, the image decoding apparatus according to anembodiment may efficiently use a memory bandwidth by setting aninterpolation tap number to a relatively small value during motioncompensation while allowing performing bi-prediction on a coding unithaving a 8×4 or 4×8 shape. For example, an interpolation filter having atap number less than 8 (e.g., a 2-tap interpolation filter), instead ofan 8-tap interpolation filter, may be used.

Also, the image decoding apparatus according to an embodiment may signalintra or inter prediction information about each region included in acurrent coding unit by splitting the region into a pre-set shape (e.g.,diagonal-based split).

The image decoding apparatus according to an embodiment may obtain aprediction sample of a current coding unit using an intra mode by usingadjacent samples of the current coding unit. In this case, intraprediction is performed by using adjacent samples that arepre-reconstructed, and the samples are referred to as reference samples.

FIG. 24 is a diagram of a reference sample for intra prediction of acoding unit, according to an embodiment. Referring to FIG. 24, for thecoding unit 2400 where a block shape is a non-square shape, a length ina horizontal direction is w, and a length in a vertical length is h, w+hupper reference samples 2402, w+h left reference samples 2404, and oneupper left reference sample 2406 are required, that is, the total numberof 2(w+h)+1 reference samples are required. In order to prepare areference sample, padding may be performed on a part where the referencesample does not exist, and a reference sample filtering process may beperformed for each prediction mode to reduce a quantization errorincluded in a reconstructed reference sample.

Although the number of reference samples when a block shape of a currentcoding unit is a non-square shape has been described in the aboveembodiments, the number of reference samples is equally applied evenwhen a current coding unit is a rectangular shape.

While this disclosure has been particularly shown and described withreference to embodiments thereof, it will be understood by one ofordinary skill in the art that various changes in form and details maybe made therein without departing from the spirit and scope of thedisclosure as defined by the appended claims. The embodiments should beconsidered in a descriptive sense only and not for purposes oflimitation. Therefore, the scope of the disclosure is defined not by thedetailed description of the disclosure but by the appended claims, andall differences within the scope will be construed as being included inthe present disclosure.

The embodiments of the present disclosure can be written as computerprograms and can be implemented in general-use digital computers thatexecute the programs using a computer-readable recording medium.Examples of the computer-readable recording medium include magneticstorage media (e.g., read-only memories (ROMs), floppy disks, or harddisks), optical recording media (e.g., compact disk (CD)-ROMs or digitalversatile disks (DVDs)), etc.

The invention claimed is:
 1. A video decoding method comprising:determining at least one coding unit by using split informationextracted from a bitstream; obtaining transform shape information aboutwhether a current coding unit from among the at least one coding unit issplit in a vertical direction or a horizontal direction or is not split,from the bitstream; determining a horizontal length and a verticallength of a transform block with respect to the current coding unitbased on transform shape information; obtaining data about a transformcoefficient from the transform block; obtaining transform kernelinformation indicating whether a non-separable transform is used; whenthe transform kernel information indicates that the non-separabletransform is used, determining a transform kernel based on thehorizontal length and the vertical length of the transform block and anintra mode used in intra prediction with respect to the current codingunit; obtaining a residual sample of the transform block for the currentcoding unit by applying inverse transformation on the data by using thedetermined transform kernel; and reconstructing the current coding unitbased on the residual sample and a prediction sample generated by theintra prediction.